XDF小蓝一道题求解

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 independent 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 make it 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. are so lacking in math skills that it will be difficult to absorb them into a city economy becoming

答案选E，但是这样lack不就作动词了吗，但是lack作动词不是不能用进行时态吗？而且一般用法是lack sth. 和be lack of sth. 吧？还有就是them是不是也是指代错误啊？becoming 和 that becomes 怎么判断？非常感谢！