The induced $emf$ can be produced in a coil by:
$A.$ Moving the coil with uniform speed inside a magnetic field.
$B.$ Moving the coil with non-uniform speed inside a uniform magnetic field.
$C.$ Rotating the coil inside a uniform magnetic field.
$D.$ Changing the area of the coil inside a uniform magnetic field.
Choose the correct answer from the options given below:

• A
  $B$ and $D$ only
• B
  $B$ and $C$ only
• C
  $A$ and $C$ only
• D
  $C$ and $D$ only