命题"若 $\alpha =\frac{\pi }{4}$，则 $\tan \alpha =1$"的逆否命题是

A．	若 $\alpha \ne \frac{\pi }{4}$，则 $\tan \alpha \ne 1$	B．	若 $\alpha =\frac{\pi }{4}$，则 $\tan \alpha \ne 1$
C．	若 $\tan \alpha \ne 1$，则 $\alpha \ne \frac{\pi }{4}$	D．	若 $\tan \alpha \ne 1$，则 $\alpha =\frac{\pi }{4}$