阅读下列短文，按要求完成各题。  

    One day an American called Simon went to London to visit his friend, Rick. Rick told him that his flat was on the first floor. When he arrived, Simon went straight to the first floor of the building. But he was told that there was no Rick on that floor. Do you know why?

    In fact, the British call the first floor of a building the ground floor. The floor above the ground floor is the first floor, which Americans would call the second floor.

The story shows that there are a few culture differences between Britain and America, though the British and Americans both speak English. The British usually hide their feelings. They seldom start a conversation with strangers. For example, on the train the British often spend their time reading newspapers or books. But Americans are quite different. They're more active and easier to talk with.

    The British and Americans may use different terms for many things. The British usually use football, eraser and mail while Americans prefer to use soccer, rubber and post.

东京时间2008年6月14日8：43，日本东北地区发生里氏7.2级地震，震源位于地下15km处。日本气象厅此次在部分区域采用“紧急地震速报”系统，为各地居民赢得了数秒不等的避震时间，从而大大减轻了地震灾害带来的损失。该图实线为地震波速度随深度的变化图，回答

如图，在四边形ABCD中，若∠1=∠2，则AD∥BC，理由是（　　）

防治沙尘暴最有效的人类行为是____。