听力原文：W: Have you ever thought about all the tons of garbage that's out in space circling the Earth？
M: Tons of garbage circling the Earth？ What do you mean？
W: I saw a television program about it last night, and according to the program, there's about 3,000 tons of metal out there in space, traveling at speeds around 17,000 miles per hour.
M: Where did all this garbage come from？
W: Well, it comes from all those space missions that have gone up since 1957. Every time a rocket ship goes up into space, it leaves a lot behind, and this stuff goes into orbit around the Earth.
M: Isn't it dangerous to have all this stuff out there？
W: Some space scientists are worried about possible collisions between this orbiting junk and spaceships, particularly manned spacecrafts; however, so far there haven't been any such accidents.
M: Well, I hope that they're going to do something about this, both for the sake of safety and for the sake of the environment.
W: Me, too. I know that right now the problem is being studied by numerous scientists; hopefully, they'll be able to find solutions before the problem gets too much worse.
What are the man and woman discussing？

A. Trash orbiting Earth.
B. A trip by an astronaut to the Moon.
C. The too much garbage on Earth.
D. Becoming space scientists.