The conference a full week by the time it ends. [ ] A．must have lastedB．will hav

by引导时间状语意思是“到……时候”，句子常用完成时，例如：We will have learned 3,000 words by the end of next term.（到下学期结束的时候，我们将学会三千个单词。）再例如：The film had been on for half an hour by the time we arrived at the cinema.（当我们到达电影院的时候，电影已经开始半小时了。）本题句子中的by the time it ends的意思是“到会议结束的时候”，所以用将来完成时。