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【单选题】

B
One night in February 1962, John H. Glenn, Jr. , flew over Australia. The man in the Mercury (水星号) capsule (太空舱) was alone, but friendly voices reached him by radio. On the dark land 100 miles below, he saw a sprinkling (零星) of lights. They marked the city of Perth, where people had turned on their lights as a greeting to him.
In Friendship 7, Glenn radioed, "Tile lights show up very well. Thank 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 eigh tracking stations. Some of them were on ships at sea. Others were in the United States.
Many of the stations had been built with the help of the other countries. These countries allowed Americans to bring in radio equipment and set it up. Without the help of such lands as Nigeria, Zanzibar, and Mexico, there would have been breaks in the worldwide radio network.
John Glenn, Jr. , was the first American to orbit the earth. Pot his flight, the tracking network covered 60,000 route miles. Five hundred people worked in the stations along the route. Since his flight, the network has grown. Today, it covers more thanlO0,000 route mi- les and has about one hundred stations. One-third of these stations arc outside the United States.
The best title of the story is ______

A.
Flights of Friendship 7
B.
Tracking Station
C.
Radio Network
D.
John Glenn
题目标签:星号水星太空舱
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【多选题】下列关于水星近日点进动说法正确的是?

A.
水星近日点每百年绕太阳前进1°33′20〃。
B.
水星近日点进动是对爱因斯坦广义相对论最好的证明之一。
C.
进动现象指得是水星近日点围绕着太阳缓慢向前运动
D.
水星进动是因为水星内侧还存在一颗小行星。

【单选题】限制酶的星号活性是指在非正常条件下,限制酶()

A.
识别和切割序列发生变化。
B.
切割活性大大提高。
C.
识别和切割序列与原来完全不同。
D.
可以任意切割DNA。
E.
只能部分切割DNA。