A proxy server acts as an intermediary between a client (like your web browser) and another server (like a website). While it processes client requests for web pages (Option B), its main purpose often revolves around enhancing security for an organization or individual. Proxy servers can filter malicious content, hide the client's IP address, act as a firewall by blocking unauthorized access to internal networks, and enforce access policies, thereby providing a crucial layer of defense against external threats and unauthorized users. They can also improve performance through caching, but security is a primary driver for their deployment.
Option B, processing client requests, is a function, not the overarching main purpose. Option C is incorrect because proxy servers do not directly process database-access requests; database servers handle those. Option D is also incorrect; TCP/IP is a suite of communication protocols that proxy servers utilize, but they do not 'provide' TCP/IP itself.