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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%

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Researchers at the Shimizu Institute in Japan believe it is possible to terraform Mars by making use of the planet’s own resources and by introducing genetically altered life from Earth. They hope these actions will speed up the terraforming process, not just by adapting Mars to support Earth-life, but also by adapting Earthlife to exist on Mars. These experts think they can use the Martian geology itself to jump-start the planet. The theory is that detonation of thermonuclear devices deep in the Martian mountains will trigger eruptions of hot magma that would melt the frozen atmosphere, thereby releasing the components necessary for life. Which of the following, if true, would most weaken the experts’ theory as explained in the last two sentences（）

A. Martian mountains are well-situated and easily accessible by remote mobility devices.
B. Similar eruptions of magma on Earth have demonstrated the ability to enable life in hostile underwater environments.
C. Mars’ frozen atmosphere lacks the critical components necessary for life.
D. Even if scientists could terraform Mars, the planet would eventually have all the same problems as Earth.
E. Thermonuclear devices would be very dangerous to send to Mars.
In Rembrandt ‘s day, many of his fellow painters portrayed their characters much like the idealized gods of Greek and Roman mythology. Rembrandt differed

单项选择题

The average (arithmetic mean) number of trees per acre in a 40-acre plot is 140. If a 10-acre section of the plot contains 90 trees per acre, how many trees are there in the remaining 30 acres

A. 5,700
B. 4,700
C. 4,200
D. 3,600
E. 2,700

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