A fleet of 100 taxis is divided into two groups of 50 cars each to determine whether premium gasoline reduces maintenance costs. Premium unleaded fuel is used in group A, while regular unleaded fuel is used in group B. The total maintenance cost for each vehicle during a one-year period is recorded. The question of interest is whether the mean maintenance cost is less for vehicles using premium fuel. To address this question, which of the following is the most appropriate type of hypothesis test?

i. A test for the difference between two population means using independent samples ii. A test for the difference between two population proportions iii. A test for the difference between two population means using matched pairs iv. A test for the difference between two population standard deviations