Final answer:
Sam's announcement of a reward for returning his lost kittens and Joe's action to return them forms a unilateral contract, where Sam's public offer was accepted through Joe's completion of the requested task.
Step-by-step explanation:
The situation presented with Sam announcing a reward for the return of his lost Siamese kittens, and Joe fulfilling the condition by finding and returning them, is an example of a unilateral contract. In this case, Sam's announcement constitutes an offer that is open to the public, where the fulfillment of the condition (returning the kittens) by Joe, or anyone else who might have done so, constitutes acceptance. This differs from a bilateral contract, where there would be a two-way exchange of promises. The announcement was not simply an invitation to treat, where further negotiation could be expected, nor was it a gratuitous promise, as there was a clear offer with an attached reward. Therefore, the correct answer is E) unilateral contract.