All flights ______ because of the snowstorm,many passengers could nothing but wait.
A.had been cancelled B.have been cancelled
C.were cancelled D.having been cancelled
请高手给个确切的答案,再为我详细的讲下,以下4个非谓语动词在什么情况下用,我老是搞不清楚,麻烦讲的详细点,我将感激不尽!