An electromagnet is built using a 9-volt battery with conducting wire connected to a switch and coiled around an iron nail. A pile of metal paper clips is moved close to the iron nail, yet no attraction is apparent between the electromagnet and the paper clips. What is the most likely conclusion to explain this result?

A. The switch is turned off.

B. The switch is turned on.

C. The paper clips are made of a nonmagnetic metal.

D. There are not enough coils of wire around the iron nail.