单项选择题A．Bob is very good at running,B．Bob works as a guard.C．Bob never skips the professor’s class.D．Bob is very smart.

单项选择题A．Forty or fifty minutes of exercise once a week.B．Twenty or thirty minutes of exercise every day.C．Fifteen or twenty minutes Of exercise five days a week.D．Thirty or forty minutes of exercise three or four days a week.