Why do the leaves on trees have different colors? What makes them change color?

Leaves use sunlight, water, and air to make food for the trees. This way of making food is called photosynthesis. Photosynthesis is important to animals as well as plants. Some animals eat plants. Other animals eat these animals. 

Summer is playtime. For the leaves of many trees, however, it's work, work, work! The Sun is shining. The leaves are making food for the trees. The trees keep more than enough food deep inside. Leaves are green in summer because they are making food. Leaves also have orange, yellow, or brown colors inside them. During summer, those colors are covered by the green color. 

Many places get colder in autumn with shorter days and longer nights. Trees get less sunlight, so photosynthesis slows down. Over time， leaves stop making the green chemical（化学物质）. The orange，yellow, and brown colors grow when that happens. 

Once it gets cold enough and ice appears at night, the trees drop their leaves. They do this to keep themselves safe. If the leaves turn to ice while still on the trees, the trees can be hurt. Trees that drop their leaves are bare（光秃秃） in winter. They use the food they save in summer to get through the cold days and nights. 

Spring comes before long. Ice and snow disappear and the rains come. The Sun shines, and tiny leaves grow from branches. Once again, the leaves use sunlight, water, and air to make food. The cycle begins again. 

Why are the leaves on trees different colors? What makes them change color? Leaves use sunlight, water, and air to make food for the trees. This way of making food is called photosynthesis. Photosynthesis is important to animals as well as plants. Some animals ea t plants. Other animals eat these animals.

Summer is playtime. For the leaves of many trees, however, it's work, work, work! The Sun is shining. The leaves are making food for the trees. The trees keep more than enough food deep inside. Leaves are green in summer because they are making food. Leaves also have orange, yellow, or brown colors inside them. During summer, those colors are covered by the green color.

Many places get colder in fall with shorter days and longer nights. Trees get less sunlight, so photosynthesis slows down. Over time, leaves stop making the green chemical. The hidden orange, yellow, and brown colors grow when that happens.

Once it gets cold enough and ice appears at night, the trees drop their leaves. They do this to keep themselves safe. If the leaves turn to ice while still on the trees, the trees can be hurt. Trees that drop their leaves are bare (光秃秃) in winter. They use the food they save in summer to get through the cold days and nights.

Spring comes before long. Ice and snow disappear and the rains come. The Sun shines, and tiny leaves grow from branches. Once again, the leaves use sunlight, water, and air to make food. The cycle(循环) begins again.

Do you know your mobile phone number well? You may sometimes find it hard to remember your number. That's because China has the longest mobile phone numbers in the world. Why is that? 

The 11 digits (数字) include three parts. Each part has a different meaning. The first three numbers tell you the mobile phone service provider (服务提供商) you are using. For example, 135 is for the China Mobile Communication Corporation (中国移动) and 186 is for China Unicorn (中国联通). The fourth to the seventh digits tell you where the number is from. And the last four digits are random (随机的). 

The main reason for using 11 digits is that we have the largest population (人口) in the world. We once had 10 numbers. But as our population grew, there were not enough numbers for us to use. So we began to use 11 digits from 1999. 

11 digits can make tens of billions of mobile phone numbers. That's enough for each person to have seven or eight phone numbers to use in China. Also, we can reuse the mobile phone numbers. Usually, the service provider will use a canceled number again after three to six months. If you call a number that you haven't called for a long time, you may find its owner has changed. 

Besides China, Britain and Japan also use 11-digit mobile phone numbers. But their numbers always start with 0. So they cannot make as many numbers as we can. Countries like the United States, Australia and India use phone numbers with 10 digits. Canada's mobile phone numbers are perhaps the world's shortest: they use seven digits. 

Every year, millions of birds are killed or hurt when they fly into buildings. Why does this happen?  Birds are flying into windows and tall buildings that are all covered by glass.

Many birds fly from one place to another. Most of the time, they live in the wild, such as forests and wetlands.  They might see small trees and flowers inside a window and want to rest on these plants. The birds do not know there is glass between them and the plants.  

Some birds fly at night. They use the moon and stars to help guide them in the right direction. Tall buildings with lights on at night can confuse（迷惑）the birds.  The birds see the light, but they cannot tell that the light is coming from inside a building. They fly toward the light and crash into a building. On many mornings, there might be several dead birds lying on the ground.

  Many office buildings now turn off their lights at night. This helps reduce the number of birds that fly into buildings and it also helps save energy.

Most kids love sweets. Why？When we eat or （喝）sweet foods, the sugar enters our blood and influences our brain. It （留下）god feelings with us, making us want more. In fact, all （美味的）foods do this, but sugar has an especially strong power. That's why doctors （总是）advise us to Early humans often had very little food, so our （身体）learned to store a lot of sugar as fat. In this way, we （节省）energy for when there was no food. But today, most people have more than enough. So it may now be harming our （健康）.

It's certain （更少的）sugar. The trouble is that, in today's world, our foods are filled with sugar. Although our （餐）look better, large amounts of sugar are often added. To solve the problem, we should take more exercise, （两次）a week at least. And remember, next time you want some cookies, eat an apple instead.

Brainstorming is the practice of coining up with ideas or solutions. But we do have some rules to follow for successful brainstorming.

Focus on quantity （数量）over quality. When it comes to brainstorming, the more ideas, the better.

Don't worry about the quality of your ideas for now. Remember that your goal is to come up with as many ideas as possible. Even if none of them are perfect, you'll still have many creative ideas to use for your final plan.

Encourage big or unusual ideas. Although unusual ideas may not be immediately practical, just creating those ideas gives your brain training. It can also help to produce creative solutions that are hard to come up with.

Don't say no to the ideas of others. You can put together the best parts of different ideas to create new, even better ones. Even if you're not brainstorming as a group, you should still think about sharing your ideas with others and asking them for their advice.

You don't have to regard yourself as a very creative person to come up with excellent ideas and solutions at once. Even if you don't find the perfect solution, just practicing it can help to improve your creativity. Put these tips together and you are sure to come up with some great ideas.