再问og12-23中的指代问题

yunshishow

23 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
其中A B选项里的it在意思上是指代discus,但是在这里 the weight of the discus  discus是所有格形式，所以It在语法上不能指代discus。这个是A B选项中it指代错误的原因么？恳请牛牛解答。

MarsTOF

非N
是

yunshishow

谢谢楼上回复哈～～～