请教一题20年前的语法题

ERIK

The (leaf-cutting) ants gather (large quantities of) leaves (which) they carry (to) their underground nests.
请问错在哪里？怎么改？谢谢！

gre3333

b: --> great quantities of

ERIK

请问为什么？有相关资料吗？谢谢！

ERIK

2008年8月第15题的题目本身就有 large quantities，所以用large是没问题的！

15. Cholesterol is present in large quantities in the nervous system, where ____ compound of myelin.

(A) it a

(B) a

(C) being

(D) it is a

我用 word 的文法检查，说要改成  which --> ,which or that  不过我不了解为什么在 which 之前加逗点和不加有什么差别？谢谢！