单项选择题

Fields found that when the bacteria accounted for 100 parts per million of the grain, the beetles' supercooling point ______.

A．rose by 4℃
B．dropped by 4℃
C．rose by 5℃
D．dropped by 5℃
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单项选择题
Which of the following statements about ice-nucleating-active bacteria is true
A．They may cool the grain to - 10℃.
B．They can weaken the beetles' resistance to coldness.
C．They can be grown on most plant leaves.
D．They are used only in biological researches.
单项选择题
According to Fields, all of the following are the advantages of his technique EXCEPT that ______.
A．it is environmentally friendly
B．it is safe to the people's health
C．it is more effective than pesticides against some insects
D．it is cheaper than pesticides
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