If the $p^{th},q^{th}$ and $r^{th}$ term of an A.P. are $a,b,c$ respectively then $a(q-r)+b(r-p)+c(p-q)=$______

Question

$\begin{array}{1 1}(A) \; abc\\(B)\;a+b+c \\(C)\;a-b-c \\(D)\;0 \end{array}$