In order not to be disturbed, he spent two hours ____ in his study.

The one _________ me is writing on the blackboard ________ the classroom

Laws are what keep society ______ and the nation atpeace.

Some students even have no idea of they are studying, so they waste much time playing.

mericans have no history while Chinese have no future sounds ________; it has raised a thought provoking question, though.