一辆汽车在高速公路上行驶，由于遇到紧急情况而刹车，以速度$v\left(t\right)=7-3t+\frac{25}{1+t}$ （t的单位：s，v的单位：m/s）行驶至停止。在此期间汽车继续行驶的距离（单位：m）是（   ）

在${\left(\sqrt[3]{x}+\frac{1}{\sqrt{x}}\right)}^{20}$的展开式中，x的幂指数是整数的项共有(    )

目前地球上被人类大量利用的淡水资源主要是（  ）

    One night in February 1962, John H. Glenn. Jr., flew over Australia. The man in the Mercury(水星) capsule（宇宙飞行容器）was alone, but friendly voices reached him by radio. On the dark land 100 miles below, he saw a sprinkling of light. They marked the city of Perth, where people had turned on their lights as a greeting to him.

    In Friendship7, Glenn radioed, “ The lights show up very well. Thank for everybody for turning them on.” His capsule raced on to the east.

    During his three orbits of the earth, Glenn could always reach one of eighteen tracking stations. Some of them were on ship at sea. Others were in the United States.

    Many of the stations had been built with the help of other countries.These countries allowed Americans to bring in radio equipment and set it up. Without the help of such lands as Nigeria（尼日利亚）, Zanzibar（尚巴西，坦桑尼亚领土的一部分）, and Mexico, there would have been breaks in the worldwide radio network.

    John H. Glenn. Jr., was the first America to orbit the earth. For his flight, the tracking network（跟踪网络） covered 60,000 route miles. Five hundred men worked in the stations along the route. Since his flight, the network has grown. Today, it covers more than 100,000 route miles and has about one hundred stations. One-third of these stations are outside of the United States.