entering
notice doing sth 注意到做某事
不明白的再问哟,请及时采纳,多谢!9. The thief was noticed _____the office building by the back door on the screen.A. enter B. enter into C. to enterD. to enter into 没有entering这个选项啊？C was noticed to do 结构 enter 及物动词，不跟into. 如： He entered the classroom. 他进了教室。