During a Test Period,an Experimental Group of 10 Vehicles Using $\alpha$

During a test period,an experimental group of 10 vehicles using an 85 percent ethanol-gasoline mixture showed mean CO₂ emissions of 667 pounds per 1000 miles,with a standard deviation of 20 pounds.A control group of 14 vehicles using regular gasoline showed mean CO₂ emissions of 679 pounds per 1000 miles with a standard deviation of 15 pounds.At $\alpha$ = 0.05,in a left-tailed test,the critical value to compare the means (assuming equal variances) is:

A) -2.508
B) -2.074
C) -1.321
D) -1.717