Rivers have been important to man （）

A．When language is a barrier, people will find other forms of communication.
B．Everybody uses only one form of communication.
C．Nonlinguistic language is invaluable to foreigners.
D．Although other forms of communication exist, verbalization is the fastest.

A．people feel cool when they are near a lake or an ocean
B．scientists can explain everything we want to know
C．scientists can explain many things but not everything
D．the salt in the ocean comes from rocks