All the tasks ______ ahead of time, they decided to go on holiday for a week.A. been fulfilledB. having been fulfilledC. were fulfilledD. had been fulfilled

步骤 1：分析句子结构
句子的主语是 "they"，谓语是 "decided"，宾语是 "to go on holiday for a week"。逗号前的部分是句子的状语，需要一个非谓语动词来修饰主语 "they"。

步骤 2：确定非谓语动词的形式
由于 "tasks" 和 "fulfill" 之间是被动关系，所以要用被动语态。同时，"tasks" 的完成发生在 "they decided" 之前，所以要用完成时态。因此，这里应该使用现在分词的完成被动形式 "having been fulfilled"。

步骤 3：验证选项
A. been fulfilled：缺少主语，不能独立使用。
B. having been fulfilled：符合语法要求，正确。
C. were fulfilled：是谓语动词，不能作为状语使用。
D. had been fulfilled：是谓语动词，不能作为状语使用。