Although commas are the most commonly correct punctuation mark on the SAT exam, they aren’t always the right option.
Commas are used to separate certain participle phrases from the rest of the sentence. A participle is a -ing or -ed verb that functions as an adjective describing a noun (ex. the running boy or a used book).
Another clue that a comma is required is the phrase “such as.” When it comes right before a list, “such as” is preceded by a comma.
However, commas should NOT be used by themselves between two independent clauses (complete thoughts with subjects and main verbs); the result is an error called a comma splice.
Incorrect comma splice:
To correct a comma splice, use a semicolon, period, or comma and FANBOYS (for, and, nor, but, or, yet, and so) conjunction between the independent clauses.