This is tricky because it is usually the case that the antecedent occurs earlier in the sentence than the pronoun. In this case, the antecedent occurs AFTER the pronoun. This is less common, but still considered correct. To quote MGMAT SC,

"The antecedent normally occurs earlier in the sentence. Rarely, the antecedent may come shortly after the pronoun (eg. After he dried his tears, Jack made a vow). However, you should usually place the antecedent first.

Therefore, it is clear that the antecedent refers to the women and men.

i think the answer should be B
in c the it says " of men.....and of the women"

the is only before women and not men. this is not parallel

can someone explain how c is the best answer?

had been in C is correct because by the time they reach adulthood they had been attacked. This phenomenon is not continue in future. This clearly defines meaning of the sentence. A phenomenon started in past and ended there by the time they reached adulthood.

In D that is close to women only and I would prefer use of who here. And again as in B were born distorts the meaning.

I am not an expert my 2 cents.

shouldnt it say 'reached' instead of reach

need an EXPERT's opinion please. Why is B wrong? why is it wrong to add "who" were born... Thank you!

Thouraya wrote:need an EXPERT's opinion please. Why is B wrong? why is it wrong to add "who" were born... Thank you!

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 the time they had reached adulthood, 98 percent of men and 75 percent of women born in country have been attacked by the birds ... verb tense is not correct. Since the bird attack happened before that men and women reached adulthood, past perfect must be used for the bird attack "had been attacked" and simple past must be used for the adulthood achievement "reached adulthood".

b) by the time they reach adulthood, 98 percent of men and 75 percent of women, who were born in the country, had been attacked by birds ... the use of the present tense makes the sentence no sensical. Since a result of a study is presented, the elements considered in the study must have shown something in the past. How can a result of a study refers to something that needs to be completed in the present "...they reach adulthood.."?

c) by the time they reached adulthood, 98 percent of men and 75 percent of the women born in the country had been attacked by the birds ... past perfect correctly used to position an event (bird attack) before the other (adulthood achievement). Simple past "reached" is correctly used as the events must be happened in the past in order to be a result of a study.

d) 98 percent of the men and 75 percent of the women that were born in the country were attacked by the birds by the time they reach adulthood ... verb tense sequencing incorrect.

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 birds ... ambiguity in the use of modifier, the meaning of the sentence is affected.