OG 103 C 选项的疑惑

103. Students in the metropolitan school district lack math skills to such a large degree as to make it difficult to absorb them into a city economy becoming ever more dependent on information-based industries.

(A) lack math skills to such a large degree as to make it difficult to absorb them into a city economy becoming

(B) lack math skills to a large enough degree that they will be difficult to absorb into a city’s economy that becomes

(C) lack of math skills is so large as to be difficult to absorb them into a city’s economy that becomes

(D) are lacking so much in math skills as to be difficult to absorb into a city’s economy becoming（E）

(E) are so lacking in math skills that it will be difficult to absorb them into a city economy becoming

C is ungrammatical because it uses lack as a noun rather than as a verb: the phrase beginning Students... becomes a dangling element, and them refers illogically to skills rather than students.

这里C的them 为什么只能指代skills 而不能指代students ?