听第二段对话，回答小题．

如图，在直角梯形ABCD中，AD∥BC，∠ABC=90°，AB=8，AD=3，BC=4，点P为AB边上一动点，若△PAD与△PBC是相似三角形，则满足条件的点P的个数是(   )

我国许多大河滚滚东流流进太平洋的主要原因是 （   ）

阅读短文，判断正误。
Dear Joe,
    How are you? My sister and I are having our holiday. Yesterday we went to the library. We got there by bus. We read storybooks and had lunch there. The food was delicious. It was cheap, too. We went shopping in the afternoon. I bought a pair of shoes. I was very tired. We are planning to learn skating and do many other things during the holiday. We are sure we'll have a good time.
    How about your holiday? Please write to me soon.
Miss you.
Alice

如图，AD是△ABC中∠BAC的角平分线，DE⊥AB于点E，S_△ABC=7，DE=2，AB=4，则AC长是（   ）