Explanation:

The correct answer is option 'C', a web server.

What is a web server?
A web server is a computer program that serves websites and web pages to users upon request. It is responsible for hosting and delivering the content of a website to users who access it through a web browser.

Function of a web server:
A web server performs the following functions:

1. Hosting: It hosts the website's files, including HTML, CSS, images, videos, and other media files.

2. Processing Requests: When a user requests a webpage by entering its URL in a web browser, the web server receives the request and processes it.

3. Retrieving Data: The web server retrieves the requested webpage and any associated files from its storage.

4. Generating HTML: If the requested webpage is a dynamic page, the web server may need to generate HTML code using data from a database or other sources.

5. Delivering Response: Once the webpage is ready, the web server sends it back to the user's web browser, which then displays the page.

6. Handling Multiple Requests: Web servers are designed to handle multiple requests simultaneously, allowing multiple users to access the website concurrently.

Why is a web server necessary for a website?
A web server is necessary to make a website accessible to users worldwide. It ensures that the website's files are stored securely and delivered efficiently to anyone who requests them. Without a web server, a website would not be able to function or be accessible to users.

Conclusion:
In conclusion, a website that can be viewed by anybody in the world is generally hosted on a web server. The web server is responsible for hosting, processing requests, retrieving data, generating HTML, and delivering the website's content to users. It plays a crucial role in making websites accessible and functional on the internet.