You _______be hungry already—you had lunch only two hours ago.

--Jack, is this your jacket?--No, it _______ be my jacket. My jacket is black but this one is blue.

--The research on the new bird flu virus vaccine is challenging and demanding. Who do you think can do the job?--________ my students have a try?

(2013·高考新课标全国卷Ⅱ)Since nobody gave him any help，he________have done the research on his own.

(2013·北京东城二次联考)—________ you interrupt now？Can't you see I'm on the phone?—Sorry，sir，but it's urgent.