The standard (68) in C language contain many useful functions for input and output ,string handling ,mathematical computations, and system programming tasks.

A．database

B．files

C．libraries

D．subroutine

Which types of portable fire extinguishers are designed for use on electrical fires?（）

A.Dry chemical and carbon dioxide

B.Foam (stored pressure) and soda-acid

C.Carbon dioxide and foam (stored pressure)

D.Dry chemical and soda-acid