ANSWER: I believe the answer is B, but I'm not sure.
If you are looking for a sentence in that paragraph to support the main idea, I think it would be "All it requires is a good pair of sneakers-no cables, stylish outfits, or weights required. The main idea is basically that walking is a good and easy way to begin exercising, and that explains it.
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.