Answer:
Mr. Van Daan is caught stealing bread in the Annex. This changes our understanding of the past food shortages in the Annex, as they may have been caused by Mr. Van Daan stealing food for himself, leaving the others without food.
The correct option is B.
You can test if there are two independent clauses by separating the clauses and seeing if they can stand alone.
They hadn't planned the trip. They returned to the store the next day and bought more peanut brittle.
Since the the two clauses can stand alone, there are two independent clauses.
Two independent clauses constitute a compound sentence.
B. A device to level uneven surfaces
(they used concrete to level the ground)