— Why didn't you stop her going swimming alone? — She had left the room I had time to do

问题补充：

— Why didn you stop her going swimming alone?

— She had left the room I had time to do it．

A. after

B. before

C. till

D. as

答案：

A. after

(答案→)B. before

C. till

D. as

解析：考查before用法。在英语中before有多种不同的翻译方法，本句中的before翻译为：还没来得及…就…；before的基本含义为:在…之前；句意：—为什么你不阻止她单独出去游泳？—我还没来得及阻止她，她就离开了房间。故B正确。