Oil : Lamp :: Wax : ?

The answer is B. Candle.

Oil is used to power a lamp, and wax is used to make a candle. Both oil and wax are flammable substances that can be used to create a light source. A lamp is a device that uses oil to create a light source, while a candle is a device that uses wax to create a light source.

Bulb is not the correct answer because a bulb is a component of a lamp, not the lamp itself. Light is not the correct answer because light is the result of the combustion of oil or wax, not the substance itself. Dark is not the correct answer because dark is the absence of light, not the substance that produces light.