Correct choice is (d) Entity-header
The best explanation: A HTTP header which does not relate to the content of message is a response-header. A request-header is used to provide information about request or response. Entity-header field defines meta information about the body. If the body is not present resource is identified by request. The general syntax for all the header fields is msg-header=field-name “:” [field-value]. General-header field is for both response and request.