Seeing the doctorUnit 3 Language in use4IhaventdonemuchexercisesinceIgotmycomputerlastyear.Ihavehadhimforthreemonthsnow.Sincethen,ithasbecomepartofmylife.Languagepracticesince常用来引导时间状语，后常接时间点或过去时的句子，该时间状语通常为完成时态的标志。since引导的时间状语从句时态为：主句完成时，since从句过去时。for后常接时间段，用来说明动作或状态持续的时间，“for+时间段”也通常为完成时态的标志。since和for在现在完成时中的应用1.Ihaventdonemuchexercise_Igotmycomputerlastyear.2.Ivebeenill_aboutthreedays!3.Wehaveplayedfootball_ayearnow.4.Scientiststhinkthattherehasbeenlifeontheearth_hundredsofmillionsofyears.5.
