Chinese astronauts have successfully grown rice seeds（種子） on the Tiangong space station and this experiment（實(shí)驗(yàn)） is important. "If we want to land on Mars，bringing food from Earth is not enough.We have to find more food for longtime space explorations（探索），" a scientist Zheng Huiqiong said.
   During the experiment，two kinds of seeds were put in the lab of the space station.It is hoped that the experiment can finish a full life "from seeds to seeds".And astronauts will collect new seeds and then ice them，before finally bringing them back to the earth for further studies.
   "China has got space seeds through the experiment in space，" Zheng said.Rice was the most important food for astronauts during the early days of space tour.The first humans to land on the moon in July 1969 ate freeze-dried chicken and rice during their trip in space.
   Over the past sixty years，scientists around the world have done lots of research on growing plants in space.And there were more than twenty experiments in spacecraft before.However，only a few plants，such as rice and beans，could grow successfully in space environments.That's because plant growth in space faces many problems such as longer flowering time and worse seed quality（質(zhì)量）.

（1）Why did scientists do the experiment of growing rice seeds on the space station？

A

A

A．To prepare for the trip to Mars.
B．To find more rice seeds on Mars.
C．To bring food from the earth.
D．To test different rice seeds on Mars.
（2）What does the underlined word" them" refer to（指代）？

C

C

A．Plants.
B．Studies.
C．Seeds.
D．Astronauts.
（3）The writer mentions the first humans to land on the moon to show

A

A

.
A．the importance of rice in space tour
B．the difficulties of space exploration
C．the special way to plant space seeds
D．the picture of landing on the moon
（4）What can we learn from Paragraph 4？

C

C

A．The cost of growing plants in space.
B．The purpose of growing plants in space.
C．The difficulties of growing plants in space.
D．The development of growing plants in space.
（5）What is the main idea of the passage？

D

D

A．Problems of plant growth in space.
B．Difficulties for further space exploration.
C．A famous scientist —Zheng Huiqiong.
D．A successful experiment on the space station.