答案：B

考查固定句式。It is/was the +序数词+time (that) sb…结构表示某人第几次做某事，如果前面是is，后面从句的谓语动词用现在完成时态；如果是was，后面从句谓语用过去完成时态。句子It was the first time中系动词是was，所以从句we _______ a film in the cinema together as a family的谓语动词要用过去完成时态。选B。