问题
下面【互为倒数的三角函数】，正确的是哪个？选项
[A]. $\begin{cases} & \tan \alpha \cdot \csc \alpha = 1; \\ & \sin \alpha \cdot \cot \alpha = 1; \\ & \cos \alpha \cdot \sec \alpha = 1. \end{cases}$[B]. $\begin{cases} & \tan \alpha \cdot \cot \alpha = 1; \\ & \sin \alpha \cdot \sec \alpha = 1; \\ & \cos \alpha \cdot \csc \alpha = 1. \end{cases}$
[C]. $\begin{cases} & \tan \alpha \cdot \cot \alpha = -1; \\ & \sin \alpha \cdot \csc \alpha = -1; \\ & \cos \alpha \cdot \sec \alpha = -1. \end{cases}$
[D]. $\begin{cases} & \tan \alpha \cdot \cot \alpha = 1; \\ & \sin \alpha \cdot \csc \alpha = 1; \\ & \cos \alpha \cdot \sec \alpha = 1. \end{cases}$
$\begin{cases} & \tan \alpha \cdot \cot \alpha = 1; \\ & \sin \alpha \cdot \csc \alpha = 1; \\ & \cos \alpha \cdot \sec \alpha = 1. \end{cases}$