选B 这是虚拟语气 第一句是过去式,宾语从句.我之前以为你明天会回来 ,当然从句用will的过去式.
第二句是条件从句.回答也是用过去式.如果我不是因为（过去）要参加会议,我过去就会回来的.排除AC.为什么不选D,是因为第一不符合语法规则,第二回答用现在时可以改成if i do not have to attend a meeting,i will come back tomorrow.这样你应该记清楚变成过去式就应该是If i didn't have to attend a meeting,I would come back= I would if I didn't have to attend a meeting.请问如果是I would(have come)if I hadn't had to attend a meeting.这样理解有问题吗?理解没问题