[单选题]
Faraday's law of inducet79o312nn 5zpc4 sd1wj u soc: y4ikk *fs 9)hlsvtmv 8c5:zhtion states that the $emf$ induced in a loop of wire is proportional to
A. the magnetic flux.
B. the magnetic flux density times the loop's area.
C. the time variation of the magnetic flux.
D. current divided by time.
