The principle under Section 55 of the Indian Contract Act, 1872 is that time is not automatically of the essence in contracts unless explicitly stated.
Option a) is correct because if the completion of work is crucial to the contract, the parties would typically not agree to an extension of time.
Option b) is correct as well, because agreeing to extend the time indicates that time was not considered essential at the outset.
Option c) is also correct, as clearly stipulating the importance of time in a contract establishes that time is of essence under Section 55.
Therefore, option d) is the correct choice, as all statements accurately reflect the application of Section 55 of the Indian Contract Act.