如需定义一个求圆面积的函数，下列函数定义哪个是正确的？

A、doubleArea(doubler){doubles;s=3.14*r*r;returns;};
B、voidArea(doubler){doubles;s=3.14*r*r;returns;};
C、doubleArea(){doubles;s=3.14*r*r;returns;};
D、doubleArea(doubler){Area=3.14*r*r;}