The answer to this problem is Indefinite Pronoun it means one may help someone either on purpose or without knowing
B is correct "Dozens" is spelled correctly. As for the other sentences their is incorrect spelling. :)
A non-restrictive modifier add information that does not restrict who the subject can refer to (compare to "The one Marlena that enjoys many subjects" -this one restricts the subject to a specific Marlena). Here it's "who enjoys many different subjects" - it adds additional information about her, but doesn't change the referent.
It shows that there are more sources for the reader to read, and it also is strong supporting evidence for the main idea.
