英语选择 选什么?4.The manager offered us a lift when he was leaving

C
解释：
句子可以看成：Walter offered us a lift when he was leaving the office,but we declined the offer.
but 后边是一个完整的句子,根据意思和形式,we declined the offer 已经是完整的了,而“工作没有完成”是我们拒绝的原因.but 是连词,后面只能是一个完整句子,所以our work 使用独立主格结构,即not having been finished
再问： 选A 可以吗？
再答： 应该选B!!!我打错了...
再问： 为什么选B啊， Walter offered us a lift when he was leaving the office,but we declined the offer已经是一个句子了。 所以 but our work _____, 就不应该是个句子呀?