The question stem tells us that either x must be 0 or else y must equal z.
Statement (1) We cannot determine whether z = 2 or x = 0 AND z = 4, so this statement alone is insufficient.
The correct answer could be B, C, or E.
Statement (2) Since , y must equal z. But without knowing the value of y, we do not know whether.
The correct answer must be either C or E.
Statement (1 & 2) The statements together tell us , so they are sufficient together.
The correct choice is C.