【题目】Mike used to be a top student, but he has fallen behind he lost himself in playing computer games.
A. afterB. since
C. whenD. until
在线课程【答案】B
【解析】
考查连词辨析。句意：迈克曾经是一名优等生，但自从沉迷于电脑游戏后，他就落后了。A. after在……之后；B. since自……以后；C. when当……时；D. until直到…时，根据题意，故选B。