Under which of the following circumstances can specific performance of a contract  not be enforced in favor of a person?

When the person has obtained substituted performance of the contract under Section 20, Explanation: Specific Relief Act: Section 16 Personal bars to relief: Specific performance of a contract cannot be enforced in favour of a person-(a) who has obtained substituted performance of contract under section 20; or (b) who has become incapable of performing, or violates any essential term of, the contract that on his part remains to be performed, or acts in fraud of the contract, or wilfully acts at variance with, or in subversion of, the relation intended to be established by the contract; or (c) who fails to prove that he has performed or has always been ready and willing to perform the essential terms of the contract which are to be performed by him, other than terms of the performance of which has been prevented or waived by the defendant.