Let $$V$$ and $$I$$ be the readings of the voltmeter and the ammeter respectively as shown in the figure. Let $$R_V$$ and $$R_A$$ be their corresponding resistances. Therefore,

A

$$R = \frac{V}{I}$$

B

$$R = \frac{V}{I - \left(\frac{V}{R_V}\right)}$$

C

$$R = R_V - R_A$$

D

$$R = \frac{V(R + R_A)}{I R_A}$$