The following figure-I .427 shows a block of mass m suspended from a fixed point by means ofa vertical spring. The block is oscillating simple harmonically and carries a charge q. There also exists a uniform electric field in the space. Consider four different cases. The electric field is zero, in case-I, `E= mg//q` downward in case-2, `E = mg// q` upward in case-3 and `E = 2mg//q` downward in case-4. The speed at mean position of block is same in all cases. Select which of the following statements is/ are correct :

Options

A. Time periods ofoscillation are equal in case-I and case-3
B. Amplitudes of displacement are same in case-2 and case-3
C. The maximum elongation (increment in length from natural length) is maximum in case-4
D. Time periods of oscillation are equal in case-2 and case-4