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

Question

$\begin{array}{1 1}(A) \; 0\\(B)\;1 \\(C)\;abc \\(D)\;pqr \end{array}$