The system of equations $x-k y-z=0, k x-y-z=0$ and $x+y-z=0$ has non trivial solutions. Then the possible values of $k$ are
(a) $\pm 1$
(b) $\pm 2$
(c) 0
(d) $\pm 4$
(a) Statement- 1 is True, Statement- 2 is True; Statement- 2 is a correct explanation for Statement- 1
(b) Statement- 1 is True, Statement- 2 is True; Statement- 2 is NOT a correct explanation for Statement- 1
(c) Statement- 1 is True, Statement- 2 is False
(d) Statement- 1 is False, Statement- 2 is True