The figure is not visible in the prompt, so the circuit topology is missing. Without the actual arrangement of the resistors, the equivalent resistance between $A$ and $B$ cannot be derived uniquely from the text alone.

However, the stored correct answer is given as A: $2R$. Since the question asks me to compare with the stored answer, I can only state the following:

1. Required information missing

   • To compute equivalent resistance, the exact circuit diagram is essential.
   • Different arrangements of identical resistors can produce different equivalents such as $2R$, $3R$, $\frac{5R}{3}$, or $\frac{5R}{2}$.

2. Comparison with stored answer

   • In absence of the diagram, I cannot independently verify the result.
   • If the official key says option A, then the claimed answer is: $R_{AB} = 2R$

3. Conclusion

   • Based only on the provided stored answer, the answer is A.
   • But this cannot be rigorously confirmed without the circuit image.