The Hypertext Transfer Protocol,the Web"s（ ）protocol,is at the heart of the Web.HTTP is implemented in two programs:a（ ）program and a server program.The client program and server program executing on different end systems,talk to each other by（ ）HTTP messages.HTTP defines how Web clients request Web pages from servers and how servers transfer web pages to clients.when a user（请作答此空）a web page,the browser sends http request messages for the objects in the page to the server.The server（ ）the requests and responds with http response messages that contain the objects.