单项选择题

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.void Area(double r){double s;s =3.14*r*r;return s;}
B.double Area(){double s;s =3.14*r*r;return s;}
C.double Area(double r){double s;s =3.14*r*r;return s;}
D.double Area(double r){Area =3.14*r*r;}