15. An awful crash between an express train and a bus _____ , however, occur the other day in Russia.A. does B. did D. has to D. had to
29. When I handed the report to John,he said that George was the person______.
28.Although _____ to stop, he kept on working.
27.The question _______ at present has something important to do with our nature.
26 .It is believed that if a book is _______, it will surely ______ the reader.
25. Many parents find it hard to _______ to their children when they are teenagers.