单项选择题
In 1980, the cost ofp pounds of potatoes was d dollars. In 1990, the cost of 2p pounds of potatoes was
dollars. By what percent did the price of potatoes decrease from 1980 to 1990
(A) 25%
(B) 50%
(C) 75%
(D) 100%
(E) 400%
(B) 50%
(C) 75%
(D) 100%
(E) 400%