1.表变化:Something/Somebody+be+quite different from what+主语+used to be The environmental situation here is quite different from what it used to be.2.表让步:由as或though引导的倒装句:n./adj./adv.+as/though+主语+其他+主句Tired as he was,he used to read something before going to bed.3.表(不)值得做某事:It be+worthwhile to do/doing sth.