What is the first request sent to start HTTP polling?
A. HTTP DELETE
B. HTTP GET
C. HTTP CONNECT
D. Upgrade request
A. Incorrect: HTTP DELETE is not used to start the WebSocket connection; it is instead used to perform a delete on a discrete item.
B. Correct: The first request to open a WebSocket connection is a standard HTTP GET. After the request is received, the browser sends a separate upgrade request.
C. Incorrect: HTTP CONNECT converts the request connection to a transparent TCP/ IP tunnel.
D. Incorrect: The upgrade request is sent after the server has responded to an HTTP GET request.