for+时间段,since+时间点,by+将来的时间,lately;recently,just,uptonow,tillnow,sofar,thesedays,inthepastfewyears/months/weeks/days,yesterday;lastweek;in1945,atthattime;once;duringthewar;before;afewdaysago;when,usedto+动词原形,be/become/getusedto+动名词doing,before,after,by,uptill,willdo.willbedoing,havebeendoing