3、China’s human spaceflight program plans to build on the success of the Shenzhou VII mission（任務(wù)）. The country will set up a simple space lab by 2011 and a station nine years later.

    The space lab will be manned for short periods. Scientists will use it to learn docking and other skills needed for long-term tasks including possibly landing on the moon.

       The United States and Russia have set up space labs since the 1970s. scientists use space labs to study space and to do experiments they cannot do on Earth.

We all know that Earth has gravity. And the force cannot be changed on the ground. But in space everything and everyone will be in a weightless condition. It is like when you are parachuting（降落傘降落）in space, but there’s no destination. So astronauts float in the spaceships , and when they drop something, that floats too. Weightlessness provides scientists the opportunity to explore gravity’s effects on the biological and physical systems.

In 1973, the United States launched its first space lab, Skylab, into orbit. Skylab carried out experiments in human behavior to study the effects of long time periods on the human body when in space.

They also learned much about solar flares（太陽耀斑）. Solar flares happen on the sun when energy explodes. The solar flares affect the areas around the Earth and when strong enough, will cut satellite communications.

Now astronauts in space labs carry out various experiments. The experiments are created by scientists around the world, but the crew on board perform and record them. These experiments include weightlessness on bacteria, the human nervous system, plants and eggs.

A NASA astronaut, Shannon Lucid once performed experiments on egg development in a space lab in 1996. The results were compared with the same egg development phases on Earth. The eggs had more abnormalities than those on Earth, but then scientists found out it was because of a radiation effect rather than weightlessness.

1．The passage mainly talks about      .

       A．space stations                                      B．space labs

       C．solar flares                                          D．weightlessness effects

2．What does the underlined word “them” in Paragraph 7 refer to ?

       A．scientists around the world                   B．human communications

       C．the crew on board                                                               D．the various experiments

3．From the passage, we can conclude that      .

       A．China will have a space station in the future

       B．the Shenzhou VII mission is cancelled

       C．the United States launched Skylab in 1973

       D．scientists will soon land on the moon