GMAT Verbal Section | Relative Pronouns

Hello gmatclub members,

during quizzing some official guide questions I stumbled across a question including relative pronouns.
Is it considered as incorrect to use e.g. "who" or "that" after a plural noun (e.g. "woman and men")?

The question was following:
The first detailed study of magpie attacks in Australia indicates that by the time they had reached adulthood, 98 percent of men and 75 percent of women born in country have been attacked by the birds.

a) by
...

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