Final answer:
Context is most helpful in understanding the word 'magnanimous' in the sentence 'Mary is magnanimous in all of her dealings with people, even when she does not know a person well.'
Step-by-step explanation:
In the sentence 'Mary is magnanimous in all of her dealings with people, even when she does not know a person well,' context is most helpful in understanding the word 'magnanimous.' This is because the surrounding words and the overall meaning of the sentence provide clues about the word's meaning.