请教一个代词指代的问题..

在新版sc159,160中有以下题目

159;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

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

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

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

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

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

In a previous design, the weight of the discus used in track competition is concentrated in a metal center, but now it is lined with lead around the perimeter, thereby improving stability in flight and resulting in longer throws.

A. In a previous design, the weight of the discus used in track competition is concentrated in a metal center, but now it is

B. According to a previous design, the weight of the discus used in track competition was concentrated in a metal center, but now it is

C. Once designed with its weight concentrated in a metal center, the discus used in track competition is now

D. The discus used in track competition, once designed with its weight concentrated in a metal center, but now

E. The discus used in track competition was once designed having its weight concentrated in a metal center and now

答案均为c,但是以159为例,they 前面没有指代对象,它的指代对象在后面,在以往做题中,均以指代不清被自己秒杀了,难道自己的这种规则本来就是错误的?还是prep的题目特点如此.?

恩,谢谢,有道理