A student made the electromagnet shown and used it to pick up one sewing pin. She then doubled the number of coils around the nail and used it to pick up two sewing pins.
How could she change the electromagnet again in order to pick up three sewing pins?
A. She could replace the 6V battery with a 3V battery.
B. She could replace the nail in the wire coil with a large steel bolt.
C. She could replace the 6V battery with a 12 V battery.
D. She could replace the nail in the wire coil with a thick roll of paper.

Correct answer is C!