Beijing is changing so rapidly that maps of the city go out of date almost ________ they are published.
A.afterB.onceC.as soon asD.since在线课程C
句意：北京变化如此之快以至于她的城市地图刚一出版就已经过时了。as soon as引导时间状语从句，意为“一……就……”；once则强调“条件”，意为“一旦”；其他两项与本题要求相去甚远。