When the girl ___ a teacher came into the classroomA sangB singsC to singD was singing
问题描述：
When the girl ___ a teacher came into the classroom
A sang
B sings
C to sing
D was singing
答
D 过去进行时 When 当....的时候
答
这是选择还是动词适当形式填空？ 总之应该是过去进行时
答
When the girl _D was singing__ a teacher came into the classroom
当女孩在唱歌时,老师走进了教室.
主句动作发生时,从句动作sing在进行,所以用过去进行时