单项选择题
A. the performance had begun B. had the performance begun C. the performance began D. did the performance begin
A．It is a kind of disease. B．It might occur to any person. C．It may be easy to cure. D．Simple factors can lead to insomni
A．the importance of teachers B．the way of writing an essay C．the problem of students’ spelling errors D．the importance of the dictionary use