why _______ you absent yesterday?a.did b.were c.was 为什么要选B,而不是A?

你可以还原一下事实，昨天，你缺席了 。You were absent yesterday.提问原因的时候用why 。所以就是 why were you absent yesterday?同意楼上说法，absent为形容词，原句中缺少be动词 只是表达一下个人简介 嘎嘎

题中absent应该是形容词,因为如果他是动词就缺宾语.做动词时应该为：
why did you absent youself yesteday?
所以原句缺动词,所以选择B
absent的用法
1.用作形容词,表示“做某事缺席”,其后常接介词 from：He was absent from school.他没有到校.有时根据不同的语境,也可能使用不同的介词：John is absent because of his illness.约翰因病缺席.He’s absent in Europe.他外出了,现在欧洲.She was absent due to illness.她因病缺席.不接介词的用法：He was absent,as is often the case.他缺席了,这是常有的事.The reason for his being absent remains a puzzle.他为什么缺席是一个谜.An average of 10 students are absent each day.平均每天有10个学生缺席.Each morning the teacher marks the pupils present,absent or late.每天早晨老师给学生记出勤情况.
2.用作动词,是及物动词,常接反身代词作宾语.表示“做某事缺席”,其后也接介词from：He absented himself from the meeting.他开会缺席.
3.点名时,若自己在场用 Here 或 Present (到,有)回答；若自己不在场,旁人可用 Absent (不在)回答.
4.注意派生词：absence n.缺席,不在.表示“做某事缺席”,其后也接介词 from：The teacher was angry at his absence from the meeting.老师对他开会缺席很生气.希望可以帮到你,