Answer:
b. A conjunction
Explanation:
Commas are used to separate items in a list or series of things. However, when these items are joined by a conjunction like or, and, or as well os, the comma is not necessary because conjunction already provides a smoother transition from one word or idea to another.
Take a look at the following examples:
The sweater is green, and blue. (Incorrect, the comma is unnecessary)
The sweater is green and blue. (Correct)
