2015年10月，NASA科学家宣布，在火星上发现疑似流动水，这些水中含有高氯酸盐、氯酸锰和高氯酸钠等成分，这项发现可能具有重大意义．请回答下列问题．

    What do you do on weekends? Some people like to stay at home, but others like to leave home and do other things. My friend, Tom works hard in a factory. He has a son and a daughter.

    On weekends, he usually does the same things. On Saturdays he washes his car and clothes. On Sundays, he goes to a farm with his family by car. His parents live there. The farm isn't very big, but there're often many things to do on the farm. The children help feed (饲养) the animals. There are many animals on the farm. You can see sheep, cows, horses and pigs. Tom and his wife help in the fields. At the end of the day, children are very tired and hungry. Tom's mother gives them a big meal. They are very happy.

声音是由物体的 ____而产生，上课时我们听到老师讲课的声音是由 ____传到我们的耳朵中．（填介质名称）

图中表示变质作用的序号是（　　）

水平抛出一个物体，经时间t后物体速度方向与水平方向夹角为θ，重力加速度为g，则平抛物体的初速度为（　　）