Henry Wadsworth Longfellow was a descendant of John and Priscilla Alden, (whose romance he celebrated) in the narrative poem "The Courtship of Miles Standish.
The answer is correct as is but why B is wrong B) he celebrated their romance.
“he celebrated their romance” is an independent clause. The sentence already has an independent clause, and it may not have another one. We join clauses with things like conjunctions and relative pronouns. “whose” is a relative pronoun. Substituting “whose” for “their” joins the clauses.
The answer you asked about (B) is what CB calls a “comma splice.” This joins two clauses, each of which is a complete sentence, with a comma. Generally, this is not permitted. If the comma after Alden were a semi-colon instead, choice B would be okay.
Thank you so much 