[单选题]
Faraday's law of inductpkj m/wil8zps1ms:x/w67ct g0 gz9p 7ion stat.t9bko b6bh:jkka / ;hes 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.
