The problem will appear_____ a different welfare system will be created. [ ]

(2011·全国卷Ⅰ)They ________have arrived at lunchtime but their flight was delayed.

Information technology is taught in most schools，__________we have entered the information society

I didn’t tell my parents that I wouldleave home–You ________ when you left home since youare living with them

________, the fire broke out in the cinema.[ ]