Detailed Instructions: Given a scientific passage and an answer, generate a question for the given answer.
Q: Passage: Besides their strength, another pro of electromagnets is the ability to control them by controlling the electric current. Turning the current on or off turns the magnetic field on or off. The amount of current flowing through the coil can also be changed to control the strength of the electromagnet. Answer: electric
A:
Electromagnets can be controlled by controlling what type of current?