题目内容：

Gardening 380 Kilometers above Earth

Astronauts have to go through physical, psychological, and technical training. They also go through training in how to care for plants. These “astronaut gardeners” share their work and living space with plants.

Taking seeds and plants along on a trip isn’t a new idea. As space trips become longer, it will be necessary to grow food in space. 1. Because of this, it’s not practical to send everything needed for a long journey, only to be used once and thrown away.

Plants can serve many uses on a space journey. They can provide more fresh things. 2. Also, plants can help to make air quality better because they produce oxygen. They can improve the quality of the air inside the spacecraft—the only air the astronauts can breathe.

3. Due to the lack of gravity in space, the oxygen that the plants produce stays around the plants. This can actually kill them, so fans are needed to circulate the air. Without gravity, roots don’t “know” to grow down, leaves don’t “know” to grow up, and water doesn’t easily travel up the roots to the leaves. 4. Besides, soil is too heavy to send to space, and special liquid gels (胶) are used to help plant growth.

Scientists are also working on the plants themselves. They are trying to make plants grow more rapidly and grow with less water and light in space, and they are looking for ways to make plants more resistant to disease. 5. Imagine that deserts may one day provide lots of fresh food for local people, saving transportation costs. Similarly, plants that are resistant to disease could provide an important food supply. With the world’s population now at seven billion (十亿) people, our astronaut gardeners may help discover ways to feed those billions.

A. Every plant grown in space must have several uses.

B. However, there are challenges with growing plants in space.

C. Such methods may result in improvements back here on Earth.

D. The cost of taking anything into space is about $22,000 per kilogram.

E. Specialized containers are being developed to help the plants grow correctly.

F. Astronauts will welcome the addition of fruits and vegetables to their diet of dry foods.

G. Currently all oxygen is taken aboard in tanks and then caught again so it can be reused.