Let S(t) be the price of a given security at time t. All of the following options have exercise time t and, unless stated otherwise, exercise price K. Give the payoff at time t that is earned by an investor who:

(a) owns one call and one put option;

(b) owns one call having exercise price K1 and has sold one put having exercise price K2;

(c) owns two calls and has sold short one share of the security;

(d) owns one share of the security and has sold one call.