A、A videotape. B、A book. C、A picture. D、An oxygen tank. C"photo enlargement"是指放大的照片，因此正确答案应该是C。

Listen to a talk given by an astronaut.
    Thank you. It’s great to see so many of you interested in this series on "Survival in Outer Space". Please excuse the cameras--we’re being videotaped for the local TV stations.
    Tonight I’m going to talk about the most basic aspect of survival--the space suit. When most of you imagine an astronaut, that’s probably the first thing that comes to mind, right? Well, without space suits, it would not be possible for us to survive in space. For example, outer space is a vacuum--there’s no gravity or air pressure; without protection, a body would explode. What’s more, we’d cook in the sun or freeze in the shade---with temperatures ranging from a toasty 300 degrees above to a cool 300 degrees below zero Fahrenheit.
    The space suit that NASA has developed is truly a marvel. This photo enlargement here is a life-size image of an actual space suit worn by astronauts on the last space shuttle mission. This part is the torso--it’s made of seven extremely durable layers. This thick insulation protects against temperature extremes and radiation. Next is what they call a "bladder" of oxygen--that’s an inflatable sac, filled with oxygen, to simulate atmospheric pressure. This bladder presses against the body with the same force as the Earth’s atmosphere at sea level. The innermost layers provide liquid cooling and ventilation. Despite all the layers, the suit is flexible, allowing free movement so we Call work.
    Another really sophisticated part of the space suit is the helmet. I brought one along to show you. Can I have a volunteer come and demonstrate?
21. What is the speaker’s main purpose?
22.What would cause an unprotected human body to explode in outer space?
23.Where is the "bladder" of oxygen located?
24.What does the speaker show the audience as she describes the main part of the space suit?
25.What will probably happen next?