The two lines whose equations are given by $x=ay+b,\:\:z=cy+d\:\:\:and\:\:\:x=a'y+b',\:\:z=c'y+d'$ are $\perp$ if

Question

$\begin{array}{1 1} (a)\:\:aa'+bb'+cc'=0\:\:\:\qquad\:\:(b)\:\:aa'+cc'+1=0\:\:\:\qquad\:\:(c)\:\:aa'+bb'+cc'=1\:\:\:\qquad\:\:(d)\:\:aa'+bb'+cc'=-1 \end{array}$