Final answer:
In the context of the angry mob, 'gesticulated' refers to making gestures, so the answer to the question is 'd. gesture'.
Step-by-step explanation:
The phrase 'The angry mob gesticulated wildly, trying to make their point', suggests that the mob used physical motions to express their thoughts or feelings. The correct answer to this is d. gesture, which is a form of non-verbal communication where bodily actions express particular messages, distinct from verbal communication. All the other options, a. motioned, b. flailed, and c. waved are synonyms or related actions but the question already provides 'gesticulated' which means 'to make gestures'. In this context, 'gesture' is the noun form of the verb 'gesticulated'.