A

In a parallel plate capacitor, when the separation between the plates is increased, work is done against the electrostatic force. The energy stored in a capacitor is given by:
U = \frac{1}{2} C V^2,
where C is the capacitance and V is the voltage across the plates.
As the separation between the plates changes, the capacitance changes according to C = \frac{\epsilon A}{d}, where A is the area of the plates and d is the distance between them. As the plates are separated, work done by the external agent can be calculated as:
W = U_f - U_i = \frac{1}{2} C_f V^2 - \frac{1}{2} C_i V^2,
where U_f is the final energy and U_i is the initial energy. Thus, looking at the options provided in the images, the work done is best represented by Option A.