Single service contract: refers to a contract in which one party only has rights and does not perform obligations, and the other party has only obligations but does not enjoy rights. Which of the following contracts is a single-service contract? ['A gives B a car.', 'A owes a debt to B, and the amount is large, so he mortgages his house to B.', "A buys B's old computer.", 'A rents two houses from B.']