39. a ______

A because of an intensive government advertising campaign.
B in response to the appearance of new varieties of pest.
C as a result of changes in the seasons and the climate.
D to ensure more cotton was harvested from each crop.

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 replacementof pesticides.

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.