The correct answer is $\boxed{\text{A. }5 \Omega}$.
When resistors are connected in parallel, the total resistance is given by the following equation:
$$R_T = \dfrac{1}{R_1 + R_2 + R_3 + …}$$
In this case, we have three resistors with resistances of 10 ohms, 15 ohms, and 30 ohms. Substituting these values into the equation, we get:
$$R_T = \dfrac{1}{10 \Omega + 15 \Omega + 30 \Omega} = \dfrac{1}{65 \Omega} = 5 \Omega$$
Therefore, the total resistance of the combination is 5 ohms.
Option B is incorrect because 10 ohms is the resistance of one of the resistors, not the total resistance of the combination. Option C is incorrect because 15 ohms is the resistance of another one of the resistors, not the total resistance of the combination. Option D is incorrect because 55 ohms is the sum of the resistances of the three resistors, not the total resistance of the combination.