[单选题]
Faraday's law of induction states t . hc9bomf;e*ez8.w ok xwg2e2f oszo2lz ky-wu4vp7-) ot- :uhat 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.
