Passage 3

Choose the best answer and complete the passage.（选择最恰当的选项完成短文）（12分）

The First Astronauts

Since the earliest times, people have looked up at the stars, the moon and the planets. Today people use modern machines 1 at the sky. This is very different from the situation 2 years ago when people could only use their eyes.Perhaps they dreamed of 3 the universe（宇宙）.

When did humans first go into space? The story began not so very long ago, 4 the first astronauts were not people—they were animals.

Scientists wanted to make travelling to space as 5 as possible for humans. So they decided to experiment with animals and test 6 in spaceflights. Insects, mice, frogs, dogs and monkeys were some of the animals that first went into space. Many of them died, but they helped to make space travel safer for humans. For their great service, we shouldn't forget these animals.

（　） 1. A. look B. to look C. looking D. looked

（　） 2. A. thousand B. thousands C. thousand of D. thousands of

（　） 3. A. explore B. to explore C. explored D. exploring

（　） 4. A. as B. or C. but D. so

（　） 5. A. safe B. safer C. safest D. the safest

（　） 6. A. they B. them C. their D. theirs