The shape of the distribution of the time required to get an oil change at a 1515-minute oil-change facility is unknown. however, records indicate that the mean time is 16.3 minutes16.3 minutes, and the standard deviation is 3.7 minutes3.7 minutes. complete parts (a) through (c). (a) to compute probabilities regarding the sample mean using the normal model, what size sample would be required? a. the sample size needs to be greater than or equal to 30. b. the normal model cannot be used if the shape of the distribution is unknown. c. any sample size could be used. d. the sample size needs to be less than or equal to 30.