问题
选择题
(2013·四川省乐山一模)The pupils were playing games in the classroom ________ a gunman entered and began shooting wildly at them.
A．while
B．when
C．as
D．before
答案
答案：B
选B 考查连词。句意：学生们正在教室做游戏，这时一名持枪的男子进来并对着他们开始疯狂扫射。连词when意为“这时”，可接短暂性动词。