During a test period, an experimental group of 10 vehicles using an 85 percent ethanol-gasoline mixture showed mean co2 emissions of 240 pounds per 100 miles, with a standard deviation of 20 pounds. a control group of 14 vehicles using regular gasoline showed mean co2 emissions of 252 pounds per 100 miles with a standard deviation of 15 pounds. a quick comparison of the sample variances suggests that the population variances are: a. probably equal. b. probably unequal. c. incomparable.