Final answer:
To apply for a commercial driver's license, typically, a full, unrestricted non-commercial license like a Class 5 is required. It's important to verify specific regional requirements, as they can vary.
Step-by-step explanation:
To apply for a commercial driver's license (CDL), you must already hold a certain class of personal driving license. The specific class required can vary based on the region or country's licensing system. In the context of this question, if options such as Class 7, Class 5, and Class 10 are given, these likely correspond to a localized licensing system.
Typically, a full, unrestricted non-commercial license is required before one can upgrade to a commercial license, which is often referenced as a Class 5 license. Therefore, the correct answer is most likely b. Class 5. However, it's essential to check the specific requirements for the region where you are applying for a CDL as these can differ.