JEE Math Practice Question

Let S be the set of all real values of k for which the systemof linear equations x + y + z = 2 2x + y $$-$$ z = 3 3x + 2y + kz = 4 has a unique solution. Then S is :

1. A.an empty set
2. B.equal to {0}
3. C.equal to R
4. D.equal to R $$-$$ {0}