Hi Jerry,

    Thank you1your invitation to2your school next week. I am sorry I3come. I'm not going to be4next week. On Monday, I have a piano lesson58:00 to 10:00 in the morning, and I have to study for the English test in the afternoon. On Tuesday, I am6a friend from my hometown at the airport. On Wednesday, I am7tennis with my friends. I have to look after my 8grandpa on Thursday. On Friday, I'm helping one of my classmates 9 his English. I am busy10week.

我国内流河和外流河的丰水期都在夏季，其主要原因是（　　）

汽车行驶的正前方有一座高山，汽车以12m/s 的速度匀速行驶。汽车鸣笛2s后，司机听到回声，则此时汽车距高山有多远?(设声音在空气中的传播速度为340 m/s)