Ans: A
$\begin{array}{rcl}
\dfrac{\cos A}{\tan (90^\circ – A)} & = & \dfrac{\cos A}{1/\tan A} \\
& = & \cos A \tan A \\
& = & \cos A \times \dfrac{\sin A}{\cos A} \\
& = & \sin A
\end{array}$
$\begin{array}{rcl}
\dfrac{\cos A}{\tan (90^\circ – A)} & = & \dfrac{\cos A}{1/\tan A} \\
& = & \cos A \tan A \\
& = & \cos A \times \dfrac{\sin A}{\cos A} \\
& = & \sin A
\end{array}$
