An emf is produced in a coil, which is not connected to an external voltage source. This can be due to 

(a) the coil is in a time-varying magnetic field
(b) the coil moving in a time-varying magnetic field
(c) the coil moving in a constant magnetic field
(d) the coil is stationary in an external spatially varying magnetic field, which does not change with time

Choose the correct option

1. (a), (b) and (c)
2. (a), (b) and (d)
3. (b), (c) and (d)
4. all of the above

(a, b, c)
Here, magnetic flux linked with the isolated coil change when the coil being in a time varying magnetic field, the coil moving in a constant magnetic field or in time varying magnetic field.