Hi All,
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 the country have been attacked by the birds.

It is very important to understand the intended meaning of the sentence to ascertain the timeline of the events. The first detailed study of magpie attacks in Australia suggests that by the time 98% of men and 75% of women reached adulthood, they had already been attacked by the bird.

Notice that the sentence says that men and women had already been attacked by the bird even before they reached adulthood. This means that they got attacked first and then they reached adulthood. Now this can be reported in two ways:
a. “by the time they reach adulthood, 98% of men and 75% of women have been attacked by the birds.” (Reported in Present context)
b. “by the time they reached adulthood, 98% of men and 75% of women had been attacked by the birds.” (Reported in Past context)
Error Analysis:
1. This sentence uses past perfect tense for the event that took place later and present perfect tense for the event that took place earlier. In order to establish the correct sequencing, we must use past perfect for the event that took place earlier, that is men and women being attacked, and simple past tense for the event that took place later, that is they reaching adulthood.
POE:
Choice A: by the time they had reached adulthood, 98 percent of men and 75 percent of women born in the country have been attacked by the birds.
Incorrect for the verb tense error discussed above.
Choice 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 the birds.
Incorrect. This choice repeats the verb tense error by using simple present tense for the event that took place later when past perfect has been correctly used for the earlier event.
Choice C: by the time they reached adulthood, 98 percent of men and 75 percent of women born in the country had been attacked by the birds.
Correct. The verb tense error has been corrected here.
Choice D: 98 percent of men and 75 percent of women that were born in the country were attacked by the birds by the time they reach adulthood.
Incorrect. a. “that” cannot be used to refer to “men and women”.
b. “reach” is not written in the correct verb tense.
Choice 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.
Incorrect. We Have modifier ambiguity in this choice. Notice that “by the time they reached adulthood” is placed little awkwardly that makes it ambiguous that which entity it’s modifying. It seems as if it is modifying “who were born in the country”. This modifier should have a comma after adulthood to do away with this ambiguity.
PS – Pronoun “they” in Choices A, B, C and E refers to “men and women” because only these men and women reached adulthood. There is no other antecedent “they” can logically refer to.

1. Use past perfect for the event that took place earlier and simple past for the event that took place later.
2. Use the correct combination of verb tenses depending upon the context of the sentence.
3. There should not be any ambiguity in modifier reference.
Hope this helps.
Thanks.
Shraddha
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