I believe the correct answer from the choices listed above is the first option. A collective subject is a noun (functioning as the subject) that describes a group made of many parts. Examples are brood of chickens, drove of cattle, gaggle of geese, nest of bees, swarm of hornets and herd of buffalo.
Answer: A
Explanation: Makes the most sense out of the others.
The phrase <em>eating a peanut butter sandwich </em>is a gerund phrase, given that the word <em>eating </em>is a gerund.