The system of linear equations <br> $x + \lambda y - z = 0$ <br> $\lambda x - y - z =0$ <br> $x + y - \lambda z = 0$ <br> has a non-trivial solution for :

Question

( A ) exactly two values of $\lambda$
( B ) infinitely many values of $\lambda$.
( C ) exactly three values of $\lambda$
( D ) exactly one values of $\lambda$