单选题
Why are there problem weeds?
A、
Because they are the weeds that cannot be eradicated by herbicides.
B、
Because all selective herbicides can encourage the growth of previously unimportant weeds by eliminating their competitors.
C、
Because they were hardly considered before so that their seeds were not prevented from germinating.
D、
Because they benefit greatly from the fertilizer applied to the farm lan
【正确答案】
B
【答案解析】
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