659. 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 (E) to act as a sentinel sounding
我认为结构是 such as A ,(同位语作为解释), andB A-defending the entrance and B-scouting outside the cave 都是名词词性,作为duty的例子 同位语-acting as sentinels and to sound a warning at the approach of danger |