Read the excerpt from the National Park Service Harry S. Truman Historical Site. "One week later, on August 14, 1945, after the second atomic bomb was dropped on Nagasaki, the Japanese surrendered. World War II, the deadliest conflict in human history, with between 50 and 85 million fatalities, was finally over.”

–National Park Service Harry S. Truman Historical Site

What is the most likely reason the US dropped a second atomic bomb on Japan?

The first bomb destroyed a city, not the Japanese army.
The US had built two bombs and had planned to use both.
Japan refused to surrender after the first bomb was dropped.
The first bomb fell in a rural area, so few Japanese were impacted.