[问答题]
List the three ways o,xu(fr*m l73s)mfhuv 9 ir:ct* 8xrck c7lf;jhat an $emf$ can be induced in a loop of wire.
参考答案: 1. by changing the magnetic field
2. by changing the area of the loop in the field
3. by changing the loop's orientation with respect to the field
