What purpose does the header() function serve in PHP?

The header() function in PHP is primarily used for sending raw HTTP headers to the client. This function enables developers to manipulate the HTTP response directly by setting headers that instruct the client (typically a web browser) on how to handle the response.

For instance, you might use header() to set the content-type of a response, indicating to the client the type of content being returned (like text/html or application/json). Additionally, it is frequently used to manage cache control or to define custom headers needed for proper functionality of the application.

Choosing option C reflects a fundamental understanding of the purpose of the header() function. While redirecting the user to a different page is a common use case for the header() function (specifically by using a "Location" header), it is only one of its many functionalities. Hence, the correct answer encompasses the broader capability of the function, which is to send any raw HTTP header, not just for redirection or cookie management.