Ans: D
$\begin{array}{cl}
& \dfrac{1}{a-2} – \dfrac{2}{1-a} \\
= & \dfrac{1}{a-2} + \dfrac{2}{a-1} \\
= & \dfrac{1(a-1)+2(a-2)}{(a-1)(a-2)} \\
= & \dfrac{a-1 + 2a -4}{(a-1)(a-2)} \\
= & \dfrac{3a-5}{(a-1)(a-2)}
\end{array}$
$\begin{array}{cl}
& \dfrac{1}{a-2} – \dfrac{2}{1-a} \\
= & \dfrac{1}{a-2} + \dfrac{2}{a-1} \\
= & \dfrac{1(a-1)+2(a-2)}{(a-1)(a-2)} \\
= & \dfrac{a-1 + 2a -4}{(a-1)(a-2)} \\
= & \dfrac{3a-5}{(a-1)(a-2)}
\end{array}$
