Ans: C
I has $x+y$ as a factor.
I has $x+y$ as a factor.
$x^2-y^2=(x+y)(x-y)$
II cannot be factorized.
III has $x+y$ as a factor.
$\begin{array}{cl}
& x(x+y)-x-y \\
= & x(x+y)-(x+y) \\
= & (x+y)(x-1)
\end{array}$
