The correct answer is D. 3128.
Squid is a caching proxy for web clients. It is a popular choice for caching proxies because it is fast, efficient, and easy to use. Squid can be used to improve the performance of web browsing by caching frequently accessed web pages. It can also be used to filter web traffic and to protect users from malicious websites.
By default, Squid listens on port 3128. This is the port that is used by most web browsers to connect to a proxy server. If you want to use Squid as a proxy server, you will need to configure your web browser to connect to it on port 3128.
The other options are incorrect because they are not the default port that Squid listens on. Option A, 4322, is the default port for the Squidguard web interface. Option B, 2314, is the default port for the Squidguard authentication server. Option C, 7334, is the default port for the Squidguard logging server. Option E, None of the above, is incorrect because it is not one of the possible answers.