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

单项选择题In C language，functions are important because they provide a way to （） code so that a large complex program can be written by combining many smaller parts.

A．modify
B．modularize
C．block
D．board

单项选择题Very long，complex expressions in program are difficult to write correctly and difficultto （）.

A．defend
B．detect
C．default
D．debug