Ans: B
$\begin{array}{cl}
& ab+ac-a^2-bc \\
= & ab – bc + ac – a^2 \\
= & b(a-c) +a(c-a) \\
= & -b ( c-a) + a(c-a) \\
= & (a-b)(c-a)
\end{array}$
$\begin{array}{cl}
& ab+ac-a^2-bc \\
= & ab – bc + ac – a^2 \\
= & b(a-c) +a(c-a) \\
= & -b ( c-a) + a(c-a) \\
= & (a-b)(c-a)
\end{array}$
