单项选择题 Nothing has ever equaled the （）and speed with which the human species is altering the physical and chemical world.

单项选择题 We all buy things on the （）of the moment; this is what the retail trade calls an “impulse “buy.

单项选择题 If I could ensue a reasonably quick and comprehensive solution to the crisis in Iraq, t would not have entitled my speech “the（）problem.”