Context: The passage below describes an experiment. Read the passage and then follow the instructions below.

Shelby built an electric circuit: she used wires to connect a battery to a light bulb, the light bulb to a small piece of copper, and the copper back to the battery. When the circuit was complete, the light turned on. Shelby observed the brightness of the light for five seconds. She then replaced the copper with a piece of iron of equal size and noted whether the light became brighter or dimmer. Shelby built three more of the same type of circuit. She repeated the tests with each circuit. Shelby recorded whether the circuits produced brighter light when the circuit included copper or when the circuit included iron.
Figure: a circuit with a battery, a light bulb, and a piece of copper.
Identify the question that Shelby's experiment can best answer.
A. Can light bulbs stay lit longer when circuits include copper or when circuits include iron?
B. Do circuits that include iron produce dimmer light than circuits that include copper?
Determine the correct option from the provided choices and reply with its corresponding letter.

B