Which state did the Americans buy from Napoleon for only 15 million dollars in the 1790s?（ ）
A、Ohio
B、Indiana
C、Illinois
D、Louisiana
【正确答案】：D
【题目解析】：Their crossing of the Mississippi in the 1790s helped persuade Napoleon to sell the Louisiana Territory to the United States for only 15 million dollars. At one stroke the territory owned by the United States almost doubled.