Fill in the blanks to complete each two-column proof.
Given: $\angle 1$ and $\angle 2$ are supplementary, and
$\angle 3$ and $\angle 4$ are supplementary.
$\angle 2 \cong \angle 3$
Prove: $\angle 1 \cong \angle 4$
Proof:
(FIGURE AND TABLE CAN NOT COPY)