Final answer:
The best synonyms for "weaken" are debilitate, enfeeble, and emasculate. These words accurately suggest making something weaker, unlike mitigate which means to make less severe.
Step-by-step explanation:
The word "weaken" means to make someone or something less powerful or less capable. When discussing synonyms for "weaken", options (a) debilitate, (b) enfeeble, and (c) emasculate all convey a sense of making someone weaker or less effective.
However, option (d) mitigate does not match as closely because it means to make less severe or painful, not necessarily weaker. Therefore, the best synonym matches for the word "weaken" would be debilitate, enfeeble, and emasculate.