Answer
Choice C.
Work Step by Step
The impedance of an R-C circuit, our model for the electrode, is
$$Z=\sqrt{R^2+X_C^2}=\sqrt{R^2+(\frac{1}{\omega C})^2}$$
As the frequency of oscillation $\omega$ is increased to a very large value, $X_C$ goes to zero. The impedance Z approaches the access resistance R.
Note: At high oscillation frequencies, the access resistance has a larger effect on the circuit than the capacitance does.
