题目内容：

    Some of the greatest problems we face today are concerned with the gradual destruction of our environment. Brown clouds; wildlife ____; polluted water. These ____ all seem so huge. So my family does what we can. We take cloth bags to stores instead of using plastic bags. We walk where we don’t have to ____.

But does it do any good?

I recently learned something about flamingos (火烈鸟). These beautiful birds gather in   ___ groups of a thousand or more. Every year, when the time ____ for migration, a few flamingos start the process by taking off from the lake. But ____ of the others seem to notice, so the tiny group returns.

However, the next day they ____ again. This time a few more struggle along with them, but the vast majority still ____ no attention, so these pioneers come back.

The ____ continues for several more days. Every time a few more birds join in but, _____ the thousands of others still take no ____, the great migration plan is once again ____.

Then one day something ____. The same small group of birds takes wing and a tiny number more join in, just as before. And this time their total number, though still quite ____, is enough to tip the balance. As one, the whole group takes flight and the migration ____. What a ____ sight it must be – thousands of flamingos taking to the sky at once!

A few can make a ____. It’s true that all of the great problems of the world have been solved because of the ____ efforts of a few.

If you believe in a cause (事业), don’t ____! Others will someday take notice and together we will ____ even our greatest problems.

1.A.protection B.extinction C.migration D.separation

2.A.questions B.costs C.examples D.problems

3.A.drive B.run C.cycle D.stand

4.A.tiny B.different C.huge D.similar

5.A.comes B.passes C.varies D.moves

6.A.all B.any C.none D.most

7.A.gather B.try C.sing D.appear

8.A.attract B.require C.escape D.pay

9.A.plan B.trend C.activity D.movement

10.A.since B.though C.unless D.while

11.A.responsibility B.notice C.chance D.measure

12.A.put off B.cut off C.carried out D.worked out

13.A.approaches B.works C.changes D.disappears

14.A.significant B.reasonable C.adequate D.small

15.A.continues B.delays C.finishes D.begins

16.A.familiar B.strange C.magnificent D.unrealistic

17.A.point B.decision C.difference D.mistake

18.A.useless B.tireless C.extra D.special

19.A.give up B.give in C.give away D.give out

20.A.identify B.understand C.predict D.solve