单项选择题

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 amount they spent on their crops.

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单项选择题

The Food and Agriculture Organisation has counted more than 300 agricultural pests which

A．are no longer responding to most pesticides in use.
B．can be easily controlled through the use of pesticides.
C．continue to spread disease in a wide range of crops.
D．may be used as part of bio-control’s replacement of pesticides.

单项选择题

The use of pesticides has contributed to

A．a change in the way ecologies are classified by agroecologists.
B．an imbalance in many ecologies around the world.
C．the prevention of ecological disasters in some parts of the world.
D．an increase in the range of ecologies which can be usefully farmed.