Which of the following contracts cannot be specifically enforced according to Section 14 of The Specific Relief Act, 1963?

Specific Relief Act: Section 14 Contracts not specifically enforceable—The following contracts cannot be specifically enforced, namely:— (a) where a party to the contract has obtained substituted performance of contract in accordance with the provisions of section 20; (b) a contract, the performance of which involves the performance of a continuous duty which the court cannot supervise; (c) a contract which is so dependent on the personal qualifications of the parties that the court cannot enforce specific performance of its material terms; and (d) a contract which is in its nature determinable.