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China sent up two manned spaceships and they were also great scientific _______ in the world.

We ________ the problem for a long time, but we didn’t reach any agreement.

Only after the woman had her own child ______how difficult it was to be a mother.

If I ruled the world，I would________ the world________ everything that is bad.

At times the balance in nature is____, resulting in a number of possibly unforeseen effects.

 —Shall I give you a ride as you live so far away?

—Thank you，________.

You’d better go there by train. The train ticket is________ the airplane ticket.

There was a________ look on his face when he met with the________ problem.

Lots of waste has been dumped into the river，which has led to________.

It is interesting how NASA(美國航空航天管理局)chose their astronauts for landing them on the moon. They chose men  26  the age of twenty and thirty-five. There were about fifty of them, Many were  27  air pilots.  28 were scientists with two or three degrees. NASA telephoned each man they were going to choose; told him the plans and the  29  they might get in. They then asked him if he was willing to be trained as an astronaut. “How could any man  30 such an exciting job?” One of them said, “Dangerous? Of course. It’s dangerous  31 most exciting”

The health and physical condition of  32 was, of course, very necessary.  33  those in very good health and physical condition were chosen.

While being trained to be astronauts. They went through many  34 . They studied the star and the moon, and they also studied geology, the science of rocks. This was necessary  35  astronauts would have to look for rocks on the moon. They would try to find rocks which might help to tell the  36 of the moon. They were all  37 to fly in helicopters （直升飛機(jī)）。These helicopters landed  38 down to give them some experience of the way the spaceship would  39 land on the moon , They were also taught the  40  facts about the conditions in space. They learnt all the technical details of the spaceships and rockets. They visited the scientists and engineers who  41 them. They visited the factories where they were  42. They learnt how every 43 of a space-ship and its instruments work. They also learnt every detail of ground-control  44 .

In a word, to be chosen as an astronaut. One must be in good health,  45  in science and good at piloting.