put call parity equation

By using Eq. 2.15, differences in the value of C_E(S, t) - P_E(S, t) are computed. (a) As shown above, if S > E, then the C_E (S, t) - P_E (S, t) difference decreases with an increase in E. Why? Is it because C_E (S, t) decreases in value? Or does P_E (S, t) increase in value? Or both? Support your answer. (b) The above analysis was done for S greater than the present value of E. Carry out the same analysis if S is less than the present value of E. That is, find what happens should i. E increase (i.e., buying options with higher strike prices), ii. should E decrease, iii. should r increase, iv. should T - t be larger, and v. should S decrease