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Directions: There are 20 blanks in the following text.For each blank there are four choices marked A,B,C and D.Choose the ONE that best fills the blank.

It is clear that some chemicals can damage the health of animals and humans.16 ,this is not the only problem that 17 be caused by the careless use of chemicals,Chemicals can also 18 the ecological(生态的) balance of the environment.If the ecological balance is disturbed,the results can be 19 serious.

The 20 of DDT illustrates(说明) the problem.DDT,a chemical which kills insects,at first seemed to be a perfect answer 21 many problems.It would control insects that caused dangerous diseases,22 insects that caused billions of dollars of damage to crops every year.Governments permitted and even 23 the use of DDT.Farmers in many countries 24 to spray(喷洒) it on their crops.The 25 results were good:Damage to crops 26 down,and profits went up.However,the chemical had effects which the scientists didn't see in 27 .First,it also killed insects which were the 28 enemies of the harmful insects and which were therefore beneficial to farmers.Second,and perhaps worse,DDT did not kill 29 harmful insect.A few insects had natural resistance(抵抗力) to the chemical.They 30 and reproduced in large numbers.In a few years there were large numbers of insects which were not 31 by DDT,and there were 32 insects which could act as natural 33 on these new “super insects.”Finally,it became clear that DDT was not solving the insect problem.In fact,it was making the problem worse.It 34 became necessary to find a second 35 for the effects of the first.

(  )16.A.Therefore B.However C.Meanwhile D.Besides

(  )17.A.can B.must C.will D.shall

(  )18.A.cause B.harm C.break D.disturb

(  )19.A.little B.much C.extremely D.hardly

(  )20.A.history B.shortcoming C.achievement D.advantage

(  )21.A.at B.for C.to D.of

(  )22.A.as well as B.as well C.but  D.also

(  )23.A.asked B.requested C.declared D.encouraged

(  )24.A.wanted B.began C.decided D.arranged

(  )25.A.fast B.immediate C.moment D.last

(  )26.A.put B.took C.broke D.went

(  )27.A.need B.turn C.advance D.vain

(  )28.A.natural B.ill C.ugly D.friendly

(  )29.A.any B.some  C.every D.all

(  )30.A.lived B.died C.cried D.survived

(  )31.A.effected B.affected C.damaged D.killed

(  )32.A.many B.a few C.a little D.fewer

(  )33.A.controls B.enemies C.choices D.means

(  )34.A.later B.then C.now D.so

(  )35.A.cause B.insect C.answer D.cure

16—20 BADCA 21—25 CADBB 26—30 DCACD 31—35 BDABD

解析:

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