The reason__________ their failure you know is they didn't get fully prepared for the experiment.
John promised his parents he _______ not smoke again, and he has not smoked ever since.
My brother left home five years ago. I _______ nothing from him up to now.
The power to our region has been _______ by the heavy snow.
______more effectively with foreign firms, many Chinese firms have turned to new technology.
Those books ______ in brown paper are for the kids so that the kids will not easily tear them up.