\text { Let } F(x)=f(9 x)-g(6 x) \text { , then: } \text { A) } F^{\prime}(x)=f^{\prime}(9 x)-g^{\prime}(6 x) \text { B) } F^{\prime}(x)=9 f^{\prime}(9 x)-6 g^{\prime}(6 x) \text {

C) } F^{\prime}(x)=f^{\prime}(9)-g^{\prime}(6) \text { D) None of them }