Many years ago, there was no light at night. They could find a place by the stars. 
| Later, people could make a map. They walked around a place and took notes. Then they drew a map. 
| Sometimes, people went to other cities. There were no planes or trains then.So they went by ship. Compass could help them at the sea. 
| Now, when people walk on the road or drive a car, they can use the BDS. It's very helpful! 
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