题目内容：

Zero gravity looks cool. But what about the thing no one likes to talk about? Yes, that is right: going to the bathroom. Zero gravity makes this everyday task quite a challenge. Astronauts have to be toilet-trained all over again.

The Apollo astronauts raised themselves off the seat of their chairs and stuck a clear plastic bag to their back sides with sticky strips. A second astronaut watched closely to be sure no waste matter escaped the seal. (You would not want that stuff floating around the cabin!) When the deed was done, the astronaut cleaned up with a piece of plastic attached to the inside of the bag, removed the bag, dropped a disinfectant(消毒剂) pill in with the waste matter, and put the whole thing, sealed, into a special container.

Donald W. Rethke, an engineer for Hamilton Standard Space Systems, developed a more private way to answer nature’s call: the space toilet. It is somewhat like the kind of toilet one would find on commercial airplanes--with unique adaptations for zero gravity, of course. For instance, it has thigh bars that keep the astronaut from floating off the seat.

The astronaut (male or female) defecates (排便) in a bag and urinates (排尿) in a hose. Solid and liquid wastes are kept separated because at least 85% of the urine is recycled and, yes, after careful filtration(过滤), used for drinking and other purposes. (Water is always in demand in space.) A vacuum sucks the waste materials into the toilet, where the waste is compacted into hamburger-like patties for easy storage. Although not exactly like an earthbound visit to the toilet, it is at the very least much more private than in the early days of space travel.

1.According to the first paragraph, the lack of the gravity can turn something as simple as _______ into a major challenge.

A. eating    B. answering nature’s call

C. sleeping    D. going to the restroom

2.How did astronauts use toilet systems in the Apollo days?

A. None of the waste was separated as it is now.

B. Solid waste was compressed and stored on board.

C. The toilet units used water to remove the waste through the system.

D. The astronauts each used their own private restroom.

3.To ensure the user remains seated, the toilet comes equipped with _______

A. a plastic bag    B. a sticky strip

C. a wide hose    D. a thigh bar

4.What can be inferred from the fact that most of the astronauts’ urine is recycled?

A. The recycled water tastes better.    B. Water is limited on the space shuttle.

C. It is very convenient to get their urine recycled.    D. Space science includes recycling urine.