According to the latest study，most traffic accidents     be prevented if drivers are careful enough．

Those who failed to get into the art exhibition ________ disappointed as many of the artists who should have appeared did not come. 

--- May I go now? --- No. You ______________ let the teacher know first.”

---Do you still remember when we went to Chong qing?----I can’t remember now but_____ sometime last summer?

As a student, you must ______ your teachers.