So many directors （）, the board meeting had to be put off.A. were absentB. been absentC. had been absentD. being absent

步骤 1：分析句子结构
句子的主干是 "the board meeting had to be put off"，表示董事会会议不得不推迟。逗号前的部分是原因，需要一个非谓语动词短语来修饰。
步骤 2：确定非谓语动词的形式
根据句子的语境，"so many directors" 和 "being absent" 之间是主动关系，且表示一种状态，因此使用现在分词 "being absent"。
步骤 3：验证选项
选项 A "were absent" 是过去时态，不符合句子的语境；选项 B "been absent" 是过去分词，不符合句子的语境；选项 C "had been absent" 是过去完成时，不符合句子的语境；选项 D "being absent" 是现在分词，符合句子的语境。