It was not until 1911, _______ the first vitamin was identified, _______ people realized the importance of it.
The _______ boy made the police and his family _______.
He did not go to school yesterday ___________the heavy rain.
Tom has gone to Shanghai,_____ is in the east of China.
__ he is young, he knows a lot.
I used to use English a lot and spent an hour each day _____ English books in the library.