Answer:
e) 98 percent of men and 75 percent of women who were born in the country, by the time they reached adulthood had been attacked by the birds.
Explanation:
If you rewrite the sentence in this way it is easier to communicate what you want to communicate, the problem is that in all the other options when you read the sentence you can get the idea that the people was attacked by the birds onces the birds reached adulthood, not the people, when rewritten like in the "E" option you dont get that confusion, that´s why that is the correct option.