Which HTTP method would you likely use to modify an existing resource?

The correct choice for modifying an existing resource is the PUT method. PUT is designed specifically for updating or replacing a resource at a specified URI. When you send a request using the PUT method, you typically include the updated representation of the resource in the body of the request. This allows the server to know what changes need to be applied to the existing resource.

In contrast, other methods serve different purposes. The GET method is used to retrieve data from a server and does not modify the resource at all. The HEAD method is similar to GET, but it retrieves only the headers of a response, again without making any modifications to the resource. Lastly, the OPTIONS method is used to describe the communication options for the target resource and does not involve modifying or creating resources. Thus, for any operation aiming to modify an existing resource, the PUT method is the appropriate choice.