Final answer:
The quotation reflecting Anne Frank and the others' primary concern in hiding is about the need for silence to avoid detection, which was crucial for their survival. Option number b is correct.
Step-by-step explanation:
The best quotation from Anne Frank: The Diary of a Young Girl that supports the answer to what is causing the most concern to Anne and the others hiding with her is B. "During the daytime we can’t make any noise that might be heard downstairs, and when someone else is there, like the cleaning lady, we have to be extra careful."
This quote directly addresses the concerns of detection and the need for secrecy in their hiding, which was of utmost importance for their survival. This constant fear of being heard and discovered was a significant source of stress for Anne and the others in hiding.