听力原文：W: What do you do for a living, Frank？
M: I am an aerospace engineer. I have been working for NASA for over fifteen years.
W: Wow, that sounds fascinating. What projects have you been involved in？
M: Well, until recently, I was heavily involved in the Cassini mission. I don't know if you're familiar with it or not. It's one of NASA's most expensive and ambitious projects. We are sending a probe to explore Saturn and its moons.
W: That sounds really interesting. Are you in any way involved in the construction of the international space station？
M: Actually, that's what I'm working on now. I'm currently a technical liaison between NASA and several European space agencies. It's an interesting job, but it can be a bit too much at times. The international space station is probably the largest international venture ever attempted, and I am constantly dealing with technical difficulties, budget problems, and delays. It's not easy coordinating the efforts of all those countries. I have been to Europe three times in the last month, and I have to go to Kazakhstan next week.
W: And I understand there's some controversy surrounding the space station. Don't some people worry that NASA is spending too much money on the project？
M: Many experts have complained that the project has grown out of control and become far too expensive. But I look at it as more than a space station; I believe it's helping to foster international scientific cooperation. It's nice to see the scientists of the world working together to create a stepping-stone to the future.
(20)

A. It plans to send a probe to explore the moon.
B. It's NASA's most expensive project so far.
C. It's an ambitious project.
D. It's involved in the construction of the American space station.