A local eat-in pizza restaurant wants to investigate the possibility of starting to deliver pizzas. The owner of the store has determined that home delivery will be successful only if the average time spent on a delivery does not exceed 37 minutes. The owner has randomly selected 21 customers and delivered pizzas to their homes in order to test whether the mean delivery time actually exceeds 37minutes. What assumption is necessary for this test to be valid?

 The sample mean delivery time must equal the population mean delivery time. None. 

The Central Limit Theorem makes any assumptions unnecessary.

 The population variance must equal the population mean.

 The population of delivery times must have a normal distribution.

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