To find the effective resistance between $A$ and $B$, the circuit diagram is required. The prompt includes only the text of the question and options, but the actual resistor network is missing.

Without the circuit configuration, the effective resistance cannot be determined uniquely, because different arrangements of equal resistors can give any of the listed values:

• $\frac{8R}{3}$
• $\frac{4R}{3}$
• $\frac{2R}{3}$
• $\frac{5R}{3}$

Therefore

The problem is incomplete as stated here, since the resistor network between $A$ and $B$ is not shown.

Comparison with stored answer

The stored correct answer is A: $\frac{8R}{3}$. Since the circuit diagram is absent, I cannot verify or derive that result from the given information alone.