单选题 Tom has been most helpful to us; in fact I don"t know what we ______ without him.
【正确答案】 D
【答案解析】[解析] 考查虚拟语气。前面的半句话用的是现在完成时，表明动作到目前为止已经完成了，故后面假设的过去的情况，用would have done。