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
-----Have our working conditions improved? ---No, ______than before, I’m afraid.
The task is too much for him, so he can’t continue ______any longer. He must get some help.
I haven’t seen______ this since I collected stamps.
I am afraid that his answer is _____ from correct.
Professor Smith has written some novels, but he is _____ known for his plays.