21. Scenario: Automotive Sport-utility vehicles (SUVs) have recently become common in American families, just as pick-up trucks have long been common. SUVs tend to be large and heavy vehicles, just like pick-up trucks, and one researcher wondered whether the fuel milage was different between these two types of large and heavy vehicles. Pick-up trucks are known to average 23.0 miles- per-gallon (mpg) on the highway with population standard deviation 4.3 mpg. The researcher sampled 50 SUV's and found an average gas milage 21.5 mpg. Conduct a hypothesis test and construct a confidence interval at significance level 0.01 . a) What is the appropriate hypothesis test procedure? a. z-Test of the Mean b. t-Test of the Mean c. z-Test of Proportion d. t-Test of Proportion