Not until ___ to do my homework ____ how much time I had wasted playing computer games.   [ ]

A. I began; I realized      

B. I began; did I realize    

C. did I begin; I realized    

D. did I begin; did I realize

过滤式防毒面具由口罩、直纹管、滤毒罐三部分组成，毒气可通过滤毒罐截留、分解或吸附。