Step 1: Understand analogy structure.
Enforce : Relax are antonyms (opposites). So the missing pair must also be antonyms.
Step 2: Check options.
(A) Allow → synonym of Permit, not opposite. ✗
(B) Forbid → opposite of Permit. ✓
(C) License → synonym of Permit, not opposite. ✗
(D) Reinforce → unrelated to Permit. ✗
Step 3: Confirm analogy.
Just as Enforce is opposite of Relax, Permit is opposite of Forbid.
Final Answer:
\[
\boxed{\text{Forbid}}
\]