若 $\triangle A B C$ 中, $C=90^{\circ}, A C=3, B C=4$, 则 $\sin (A-B)$ 的值是 ( D )
[解析]由条件可知 $\cos A=\frac{3}{5}, \sin A=\frac{4}{5}, \sin B=\frac{3}{5}, \cos B=\frac{4}{5}, \therefore \sin (A-B)=\sin A \cdot \cos B-\cos A \cdot \sin B=\frac{4}{5} \times \frac{4}{5}-$ $\frac{3}{5} \times \frac{3}{5}=\frac{7}{25}$.