If S is the set of distinct values of 'b' for which of the following system of linear equations <br> $x + y + z = 1$ <br> $x + ay + z = 1$ <br> $ax + by + z = 0$ <br> has no solution, then S is :

Question

( A ) a singleton
( B ) an empty set
( C ) an infinite set
( D ) as finite set containing two or more elements