Which of the following is the highest fee among the following licenses and tests?

The highest fee among the options is associated with the CDL skills test. This test evaluates a commercial driver's ability to operate a commercial vehicle safely and competently. Given the specialized nature of commercial driving, the skills test is more comprehensive and requires a higher level of training and evaluation compared to the other options listed.

In contrast, the CDL knowledge test and the provisional Class D Utah license involve different scopes of testing that generally incur lower fees. The extension of a license by mail typically involves a minimal administrative fee. Since the CDL skills test emphasizes practical application and in-depth evaluation for safety on the road, it reflects a higher fee to cover the resources and administrative costs involved in conducting thorough assessments for commercial drivers.