Question

Gregor later helped support Theresia’s three children (two of ____ eventually became doctors).

Answer 1

Whom is the best choice

Answer 2

Answer: whom

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Which is used to refer to things. Who and whom are used to refer to people. Use who as a subject, and whom as the object of a verb or with a preposition. The preposition, in this case, is "of," which means that "whom" would be the correct answer.