**Solution:**

**Particular enunciation:** Let AB||CD and transversal PQ intersects them at E and F respectively. On one side of the transversal PQ the interior angles be ∠BEF and ∠EFD and on the other side the interior angles be ∠AEF and ∠EFC.

**Proof:** ∠EFD = Corresponding angle ∠PEB.

Now, ∠BEF + ∠EFD = ∠BEF + ∠PEB; [∠EFD = Corresponding angle ∠PEB]
= ∠PEF

= 1 straight angle

=2 right angle.

∵ If the sum of two angles is equal to 2 right angles then they are supplementary.

∴ ∠BEF and ∠EFD are supplementary.

Similarly it is shown that ∠AEF and ∠EFC are also supplementary. **(Proved)**