阅读理解。
There are some easy things you can do to protect the environment and the earth. Choose ideas from the
list or come up with a few of your own.
●Plant flowers, grass or trees.
●Whenever you visit a park or beach, take away what you bring there-keep rubbish in a bag until you can
put it in a dustbin.
●Turn off the lights, TV sets when you leave the room. This saves a lot of electricity.
●Turn off the tap when you brush your teeth. You can save some water by not letting it run. Also, use a
glass cup instead of a paper cup because this saves paper.
●Keep the doors and windows closed in winter to keep warm air in.
●Give your old books and magazines to a library instead of throwing them away.
●Give your old clothes to poor children you know instead of throwing them away.
●Use both sides of paper.
●Stop pouring dirty water into the rivers or the lakes nearby.
●Encourage all your friends to do the same things you do to help protect the earth.
You don't have to wait until Earth Day to do these things. Make every day Earth Day.
If everyone makes a contribution to protecting the environment, the world will become much more beautiful.
1. From the above, we know that this is _____.
A. a sign
B. a notice
C. an advertisement
D. a proposal
2. The writer tells us _____.
A. to throw rubbish into a dustbin
B. to pour dirty water into the river
C. to save water by letting it run while we are brushing our teeth
D. that we can't do all these things until Earth Day
3. We can _______ to save paper.
A. use a paper cup
B. use both sides of paper
C. give old books to a library
D. pick up waste paper at school
4. Which of the following is WRONG according to the writer?
A. Turn off the lights when you leave the room.
B. Close the doors in winter.
C. Use a paper cup when you brush your teeth.
D. Give your old clothes to the poor children.
5. The main idea of this passage is how to _____.
A. save money
B. save water and electricity
C. make better use of old things
D. protect the earth
倍
，则小星间万有引力为F=Gmm/a2，母星和小星间万有引力为9F=GMm/r，则M=3m，C正确；小星受到的万有引力合力为2Gmm/a2，