[求助]OG11 118再求助，og的解释错了吗？

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

我有两个问题：1、为什么后面becoming用了进行时，前面的lack就一定要用进行时，怎么判断是进行状态？人们一般用lack不都是用一般现在时吗？某人缺少某物，哪有说某人正在缺少某物的。

2、OG的解释说：The sentence reveals an ongoing situation (the economy is becoming……), so the use of the present progressive tense(are lacking in) in place of the present tense (lack) is appropriate.按照这种解释，are lacking in中的lack就是动词了，但查了几个字典也没查到lack有这种用法，除了be lacking in，其中lacking是形容词。是OG解释错了吗？看了好多旧帖，但还是好不明白，希望有高手可以解释一下。