i=2; a=2i; b=2*i; c=2*sqrt(-1); 程序执行后a, b, c的值分别是

A、a=4, b=4, c=0.0000+2.0000i;
B、a=4, b=0.0000+2.0000i, c=0.0000+2.0000i;
C、a=0.0000+2.0000i, b=4, c=0.0000+2.0000i;
D、a=0.0000+2.0000i, b=0.0000+2.0000i, c=0.0000+2.0000i