# The system of equations $ax+y+z=0; x+by+z=0; x+y+cz=0$ has a non-trivial solution then $\large\frac{1}{1-a}+\frac{1}{1-b}+\frac{1}{1-c}=$
$\begin{array}{1 1}(1)1 & (2)2 \\ (3)-1 & (4)0\end{array}$