maxim and aphorism – both mean ‘some pithy observation containing a general truth’ -- example "The child father to the man". So both are synonyms.
The meaning of the options are
A. maximum and optimum – mean the highest level and most favourable level respectively
B. prophecy and doom – prediction and destruction respectively
C. theorem and proof – a truth established by means of accepted truths and confirmation respectively
D. precept and axiom – general rule and general truth respectively. Both are synonyms.
So option D is the answer