You currently hold a call option with a strike price of $50 and a maturity of 3 months. Which of the following positions can be combined with your current holdings to form a calendar spread? a. Long a call with a strike price of $45 and a maturity of 3 months. b. Short a call with a strike price of $50 and a maturity of 1 month. c. Short a call with a strike price of $45 and a maturity of 3 months. d. Long a call with a strike price of $50 and a maturity of 1 month.