Ans: A
$\begin{array}{rcl}
\dfrac{-k}{1-k} – \dfrac{1}{k-1} & = & \dfrac{-k}{-(k-1)} – \dfrac{1}{k-1} \\
& = & \dfrac{k}{k-1} – \dfrac{1}{k -1} \\
& = & \dfrac{k-1}{k-1} \\
& = & 1
\end{array}$
$\begin{array}{rcl}
\dfrac{-k}{1-k} – \dfrac{1}{k-1} & = & \dfrac{-k}{-(k-1)} – \dfrac{1}{k-1} \\
& = & \dfrac{k}{k-1} – \dfrac{1}{k -1} \\
& = & \dfrac{k-1}{k-1} \\
& = & 1
\end{array}$
