题目内容

21. Bio-control is free from danger under certain circumstances.

A. YES
B. NO
C. NOT GIVEN

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20. Biological control entails using synthetic chemicals to try and change the genetic make-up of the pests' offspring.

A. NO
B. NO
C. NOT GIVEN

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19. A number of pests are now born with an innate immunity to some pesticides.

A. YES
B. NO
C. NOT GIVEN

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18. Disease-spreading pests respond more quickly to pesticides than agricultural pests do.

A. YES
B. NO
C. NOT GIVEN

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17. By the mid-1960s, cotton farmers in Central America found that pesticides

A were wiping out 50% of the pests plaguing the crops.
B were destroying 50% of the crops they were meant to protect.
C were causing a 50% increase in the number of new pests reported.
D were costing 50% of the total amountthey spent on their crops.

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21. Bio-control is free from danger under certain circumstances.

A. YES B. NO C. NOT GIVEN

20. Biological control entails using synthetic chemicals to try and change the genetic make-up of the pests' offspring.

19. A number of pests are now born with an innate immunity to some pesticides.

18. Disease-spreading pests respond more quickly to pesticides than agricultural pests do.

17. By the mid-1960s, cotton farmers in Central America found that pesticides

A. YES
B. NO
C. NOT GIVEN