The pilot of a small aircraft with a 40-gallon fuel tank wants to fly to Cleveland, which is 480 miles away. The pilot recognizes that the current engine, which can fly only 8 miles per gallon, will not get him there. By how many miles per gallon must the aircraft’s fuel efficiency be improved to make the flight to Cleveland possible ？（）

A. 2

B. 4

C. 12

D. 40

E. 160

含油饱和度指的是原油在岩石中占岩石体积的百分数。（）