A．The use of insecticides should be limited and controlled.
B．A combination of some insecticides should be used at the same time.
C．New insects should be introduced to mate with those that have survived from a certain kind of insecticide.
D．New kinds of insecticides should be explored and developed.

A．There are many forms of communication in existence today.
B．Verbalization is the most common form of communication.
C．Ideas and thoughts can be transmitted by body language.
D．The deaf and the mute use an oral form of communication.