One night in February 1962, John H. Glenn. Jr., flew over Australia. The man in the Mercury  capsule 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 , Zanzibar(,), 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  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. This passage is mainly about  _  .
talking to ships at sea around the world breaks in the worldwide network the first American to orbit the earth a satellite which fell into the ocean
Question: One night in February 1962, John H. Glenn. Jr., flew over Australia. The man in the Mercury  capsule 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 , Zanzibar(,), 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  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. This passage is mainly about  _  .
A. talking to ships at sea around the world
B. breaks in the worldwide network
C. the first American to orbit the earth
D. a satellite which fell into the ocean
Answer: