1. Interpret the standard 5-resistor bridge network

   The figure referred to in this common problem is the symmetric bridge made of five equal resistors $R$ between terminals $A$ and $B$:

   • two resistors on the top branch,
   • two resistors on the bottom branch,
   • one resistor connecting the midpoints of the top and bottom branches.

   Since all five resistors are equal, the network is symmetric about the horizontal line joining $A$ and $B$.

2. Use symmetry

   Let the midpoint of the top branch be $P$ and the midpoint of the bottom branch be $Q$.

   Because the top and bottom branches are identical,

   • the potential at $P$ equals the potential at $Q$.

   Therefore, the resistor connected between $P$ and $Q$ has no potential difference across it, so no current flows through it.

   Hence, that middle resistor can be ignored for equivalent resistance calculation.

3. Reduce the circuit

   Now the circuit becomes two separate branches between $A$ and $B$:

   • Top branch: two resistors in series $\Rightarrow R + R = 2R$
   • Bottom branch: two resistors in series $\Rightarrow R + R = 2R$

   These two branches are in parallel.

4. Compute the equivalent resistance

   $R_{AB} = (2R) \parallel (2R)$

   $R_{AB} = \frac{(2R)(2R)}{2R+2R} = \frac{4R^2}{4R} = R$

5. Check options

   • A: $\dfrac{3R}{2}$ — incorrect
   • B: $\dfrac{R}{2}$ — incorrect
   • C: $2R$ — incorrect
   • D: $R$ — correct

Therefore, the net resistance between $A$ and $B$ is

$\boxed{R}$