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:
\[
\boxed{\text{Forbid}}
\]

Given an open-loop transfer function \(GH = \frac{100}{s}(s+100)\) for a unity feedback system with a unit step input \(r(t)=u(t)\), determine the rise time \(t_r\).
Consider a linear time-invariant system represented by the state-space equation: \[ \dot{x} = \begin{bmatrix} a & b -a & 0 \end{bmatrix} x + \begin{bmatrix} 1 0 \end{bmatrix} u \] The closed-loop poles of the system are located at \(-2 \pm j3\). The value of the parameter \(b\) is: