[单项选择]

Passage 4
Eating in space is different from eating on earth. The food that astronauts carry with them does not look like the food you eat. Some food is carried in closed bags. It is cooked and frozen before the astronauts get it. All the water is removed from the food. In the spaceship the astronaut puts the water back. He "shoots" hot or cold water into the food bag with a special gun. He eats the food through a small hole in the bag.
Other foods come in bite size. The astronaut puts a whole piece in his mouth at once. There can be no crumbs. Crumbs would float around the spaceship and get in the way. Meat and cake often come in bite-sixed pieces. Astronauts can’ t drink water from open cups. The water would float in drops in the air. The water is put in the special gun. The astronaut shoots the water into his mouth. Eating in space is not easy. Astronauts must learn this way.

The main idea of the whole story is that （）
A. there is more food and water in space than on earth
B. eating and drinking in space is a special problem
C. astronauts can never eat or drink in a spaceship
D. there is no food or water in a spaceship