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.
3. 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
it depends. in this case, i think both are correct, even though i prefer the first, because "such as" is on "duties". however, you should try to avoid using "such" in front of any adj.
duties such as defending the entrance, acting as sentinels and sounding a warning at the approach of danger, and scouting outside the cave for new food and roosting sites.
应该变成
duties such as defending the entrance, acting as sentinels, sounding a warning at the approach of danger, and scouting outside the cave for new food and roosting sites. 了吧?