Python is the correct answer because it has powerful libraries such as Beautiful Soup and lxml, which are specifically designed for parsing and interacting with HTML and XML documents. These libraries make it easy to navigate the document tree and retrieve the information needed, such as form field names. Perl, while powerful in text manipulation, does not have as streamlined libraries for parsing HTML as Python. Ruby and JavaScript can also be used for parsing HTML, but Python's libraries and widespread usage for such tasks generally make it a more efficient choice in scenarios involving HTML parsing in penetration testing.