It has been years ________ I returned home.
A、afterC
译文：我回家已经有好几年了。此题考查连词since的用法。since表示“从(过去某事)以来，以后或到现在”时，主句多用完成时态。又如：WherehaveyoubeensinceIlastsawyou?自从我上次见到你以后，你到哪去了?
Generally,adictionarycoversthefollowingcontentsEXCEPT______.
Fromtheviewpointofwordformation,theword“smog”isa______.
Amongthefollowingwords,“______”containsanegativeprefix.
Ifyoutrytolearntoomanythingsatatime,youmayget________.
Onecanfigureoutthemeaningof“airmail”tobe“mailbyair”byits______.
