6. The farmer ______________ in the field when he saw a UFO.
A. is working B. was working C. worked D. works
7. A ______________ has a great view of the stars, so many scientists want to work on it.
A. gravity B. cloud C. temperature D. space station
8. Scientists float in a space station because there’s no ______________.
A. technology B. science C. gravity D. air
9. Jane’s mom: In 2100, there will be many space stations near Earth.
Jane: ______________
A. Really? Why will you
go there?

B. What a good journey! C. I don’t know when they

will come.

D. Oh, it will be much easier
to explore space.
10. The world’s ______________ is growing more quickly every year. Our planet is becoming more and more crowded.
A. pollution B. popularity C. population D. pollutant
11. NASA is now working hard to ______________ whether there is life on Mars.
A. discover B. collect C. experience D. accept
12. Humans can’t live unless they have enough ______________ to breathe.
A. water B. planets C. food D. oxygen
13. Scientists have spent years ______________ information about UFOs.
A. collecting B. to collect C. collected D. collect
14. Some scientists say that flying saucers might be people's ______________.
A. imagination B. imagine C. imaginative D. imaginary
15. When you are in orbit, you'll be out of the earth's ______________ and you're weightless.
A. outside B. gravity C. atmosphere D. outskirt