Answer:
B. Japan refused to surrender after the first bomb was dropped.
Step-by-step explanation:
The United States dropped the first bomb in hopes that this would swiftly end a long, terrible war that had stretched on longer than it needed to. The USA gave Japan the Potsdam Declaration, which said they could completely surrender or face total destruction. So after Japan still did not surrender after the first bomb was dropped, the second was dropped. This is what caused Japan to finally surrender and end the war.