Marigold owns 500 shares of Borax Ltd., which currently trades at $11.75 per share. Eugene is an avid reader of the financial press and he expects the price of Borax to increase to at least $18 by the end of the year. Marigold does not expect the price of the shares to change by that much. So, she offers to sell Eugene her 500 shares at any time during the next four months at $14.75 for a premium of $1.00 per share.

If Eugene decides to accept the offer, what has he purchased?