The new rule has been working effectively since it __________.
He could have helped us, but he ____ from coming in time by a traffic jam.
____ the rain falling so hard, it becomes more and more difficult to carry on the rescue work.
The class _____ 80 students is hard to manage.
----Who do you think should answer for Li Tianyi’s behavior? ----Actually, I think it is their parents _____.
If you are in a warmer place and can get your skin _____ to the sun for 20 minutes per day, you will need less vitamin D. A. exposingB. being exposed C. been exposed D. exposed