Formula used: emf is given by

Where v is the speed

B is the magnetic field

l is the length

That above formula states that an emf induced by moving a conductor of length l with some velocity v in a magnetic field B.

Where is the electric flux through the conductor

emf induced in the conductor

Formula (2) states that an emf can be induced by changing the magnetic field that causes the change in flux through a conductor in a loop.

So option A is the answer.