You are interested in using linear regression to test whether drinking a protein shake improves weightlifting performance. From a sample of 200 college students, you estimate a linear regression with WEIGHTLIFT as the dependent variable and PROTEIN as the independent variable and find the slope of the line of best fit equals zero. Choose the best interpretation of this evidence: Drinking protein shakes has no measurable effect on weightlifting performance. Drinking protein shakes has no measurable effect on weightlifting performance, and that proves protein shakes are not beneficial to weightlifting performance. Drinking protein shakes has a positive measurable effect on weightlifting performance. Drinking protein shakes has a positive measurable effect on weightlifting performance, and that proves that protein shakes are beneficial to weightlifting performance.