Anonymization (in terms of databases) is simply replacing real data with dummy data.
Data masking is solely referring to substituting a generic character for a real one, done x amount of times as in ***-***-1234 for a phone number OR ***** as a zip code.
You cannot develop an algorithm for determining if a phone# is valid or not or if a zip code is valid or not. You cannot do lookups, test regular expressions, or really do anything useful as a developer with masked data.
I've never heard of Data Masking as replacing original data with fake data, but unfortunately, this is the only correct answer for this exam as Data Anonymization as an answer is missing on this same question (CompTIA is tricky and often you will find a slightly different set of answers that correspond to the same question). In another's exam dump, "Data purge" is substituted for "Data Anonymization", so whatever you do, don't pick A.