659 of 987, thanks again!

snowflower

1.        Some bat caves, like honeybee hives, have residents that take on different duties such as defending the entrance, acting as sentinels and to sound a warning at the approach of danger, and scouting outside the cave for new food and roosting sites.

(A) acting as sentinels and to sound

(B) acting as sentinels and sounding

(C) to act as sentinels and sound

(D) to act as sentinels and to sound（B）

(E) to act as a sentinel sounding

知道是在考并列结构，但是不是说doing A, doing B, doing C, and doing D才对吗？可是这里是doing A, doing B and doing C, and doing D, 糊涂了

，

LES

这是大并列里面套小并列。

snowflower

LES JJ，你的意思是说这里 defending 和 scouting并列，acting和sounding并列？那就是说acting and sounding是修饰前面defending的？

LES

偶的理解是这样的。但是OG的意思是acting 和 sounding 是一个小并列，然后和 defending, scouting 构成三个大并列。还请NN来解释一下。