A system X is neither in thermal equilibrium with Y nor with Z. The systems Y and Z

If thermal equilibrium exists between two systems means that those two systems are at the same temperature as that there is no heat exchange in between them.

Given that the system X is not in equilibrium with either Y or Z. If the relation between Y and Z given, we can state (b). But So we cannot say exact equilibrium condition between the systems.

Thus, due to insufficient information option (c) is correct.