The correct answer is A. does.

Here's the breakdown:

* "Adam is one of the boys who always" indicates that Adam is part of a group of boys who share a certain characteristic.
* The verb should agree with the subject, which is "Adam". Since "Adam" is singular, the verb should also be singular.
* "does" is the correct singular form of the verb "do" in the present tense.

Therefore, the complete sentence is:

* "Adam is one of the boys who always does good work."