By the time he arrives in Beljig, we_here for two days.
A. will have stayed B have been staying C shall stayD. have stayed
为何选A而不是选D期望大伙拿能给予一些建议（本人英语新手，莫要过于深奥）
假如By the time 引导的句子用一般目前时，主句应该用以后完成时（若是 be 动词，用一般以后时）；假如By the time 引导的句子用一般一般过去时，主句应该用过去完成时（若是 be 动词，用一般过去时）。比如：
By the time you come back, Ill have done my homework.在你回来以前，我的作业会都做完的。（摘自赵振才编著：《英语容易见到问题解答大词典》增订版第五版 p.225）
By the time I got to the station the train had already gone.我到达火车站时，火车已经开走了。（同上）
Ill be in bed by the time you get home. 等你到家时我已经上床睡觉了。/By the time that the guards realized what was happening, the gang were already inside the bank. 等到保安了解过来发生了什么事时，劫匪已经进了银行。（摘自《牛津英语使用方法指南》第四版414.1）
