Ans: C
$\begin{array}{cl}
& a^2-b^2+2b-1 \\
= & a^2-(b^2-2b+1) \\
= & a^2-(b-1)^2 \\
= & [a+(b-1)][a-(b-1)] \\
= & (a+b-1)(a-b+1)
\end{array}$
$\begin{array}{cl}
& a^2-b^2+2b-1 \\
= & a^2-(b^2-2b+1) \\
= & a^2-(b-1)^2 \\
= & [a+(b-1)][a-(b-1)] \\
= & (a+b-1)(a-b+1)
\end{array}$
