Everyone here will thank the firefighters for the things they have done to prevent fires _______ the environment safer.

A．make

B．to making 

C．to make

D．from making

下列程序的输出结果是
#include"stdio.h"
#define M(x，y) x%y
main()
int a，m=12，n=100；
a=M(n，m)；
printf("%d\n"，a--)；

A．2

B．3

C．4

D．5