A、Measure the speed of wind. B、Give warnings of danger. C、Pass on secret messages. D、Carry ropes across rivers. D文章提到风筝的几种用途，比如在

No one knows for sure just how old kites are. In fact, they have been in use for centuries. 25 centuries ago, kites were well known in China. These first kites were probably made of wood. They may even have been covered with silk, because silk were used a lot at that time. Early kites were built for certain uses. In ancient China, they were used to carry ropes to cross rivers. Once across, the ropes were tied down and wooden bridges would hang for them. Legend tells of one general who flew musical kites over the enemies’ camp. The enemy fled, believing the sounds to be the warning voices of angels. By the 15th century, many people flew kites in Europe. Marco Polo may have brought the kite back from his visit to China. The kite has been linked to great names and events. For instance, Benjamin Franklin used the kite to prove that lightning is electricity. He flew the kite in the storm. He did this in order to draw lightning from the clouds. He tied a metal key and a strip of silk to the kite line. The silk ribbon would stop the lightning from passing through his body. Benjamin’s idea was first laughed at. But later on, it enlightened the invention of the lightning rod. With such grand history, kite flying is sure to remain an entertaining and popular sport.
16. What does the speaker say about kites?
17. What did ancient Chinese use kites to do?
18. Why did Benjamin Franklin fly a kite in the storm?