单选题
In 1980, the cost ofp pounds of potatoes was d dollars. In 1990, the cost of 2p pounds of potatoes was 
【正确答案】
C
【答案解析】Since, in 1990, 2p pounds of potatoes cost [*] dollars, p pounds cost half as much: [*][*] or 25%, as much as the cost in 1980, which represents a decrease of 75%.
**In this type of problem it is often easier to use TACTIC 2, Chapter 11. Assume that 1 pound of potatoes cost $100 in 1980. Then in 1990, 2 pounds cost $50, so 1 pound cost $25. This is a decrease of $75 in the cost of 1 pound of potatoes, and
[*]
**In this type of problem it is often easier to use TACTIC 2, Chapter 11. Assume that 1 pound of potatoes cost $100 in 1980. Then in 1990, 2 pounds cost $50, so 1 pound cost $25. This is a decrease of $75 in the cost of 1 pound of potatoes, and
[*]