You own a stock at price S0, and buy put options on the stock at strike price X1, where X1 < S0. Further, you write call options at strike price X2, where X2 > S0. You use FLEX options in the marketplace, choosing X2 such that its call premium C(X2) exactly equals the purchased put premium P(X1). This trading strategy is called a .

A) butterfly spread

B) zero cost collar

C) short calendar spread

D) combination bear-bull spread

E) short strangle