theroomisintheterriblemess,itcannothavebeencleaned.为什么用cannothavebeen
Withalltheworkonhand,hecouldnothavegonetothecinemalastnight.为什么用couldnothavegone而不用shouldnothavegone.
Evewaslateforclassagain,sheshouldhavegotup.为什么用shouldhavegotup而不用mustgetup如果mustgetup中变成mustbegetup可否
youshouldbearinmindthatheisnotsostrongasheusedtobe为什么用usedtobe而不用wasusedtobe