Data Sufficiency (DS) | Re: Does x = y? (1) z = u (2) ABCD is a parallelogram

S1 - z=u
But we don't know anything else, x and y could be or could not be equal.
Insufficient.
S2 - ABCD is a parallelogram and AC is the diagonal.
Therefore, y=u and x=z (Alternate angles of a line intersecting two parallel lines are equal)
But we don't know if x=y
Insufficient.

Combining S1 & S2, x=z=u=y
Sufficient
Answer C.
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