To answer this question, you need to understand the concepts of grey-box testing, black-box testing, and white-box testing.
Grey-box testing involves having partial knowledge of the internal workings of the software being tested. Testers have access to some information about the underlying code, such as design documents or limited access to the source code. However, they do not have complete knowledge or visibility into the entire codebase.
Black-box testing, on the other hand, is a testing approach where the tester has no knowledge of the internal workings of the software being tested. Testers only have access to the inputs and outputs of the software and do not have any information about the underlying code or implementation details.
In this question, the scanning of the underlying source code with a database of regular expressions to quickly identify suspicious code, application inputs, outputs, etc., primarily relates to white-box testing. White-box testing is a testing approach where the tester has full knowledge and visibility into the internal workings of the software being tested. Testers have access to the source code and can analyze it to identify potential vulnerabilities, security issues, or other potential problems.
Therefore, the correct answer is C) White-box testing.