Peru, a country ____ the Pacific coast of South America, gained its independence ______ Spain in 1821.

A．off; from

B．along; of

C．on; of

D．on; from

以下程序的运行结果是______。
#define A 4
#define B(x)A*x/2
main()
float c，a=8.0；
c=B(a)；
printf("%f\n",c)；