The doctor must be _______ 24 hours a day, 7 days a week in the boarding school.
I’ m sorry, I mistook you ___ your sister ___ mistake.
The scientists are trying to ___ natural energy to decrease air pollution.
China is ___ the east of Asia while Japan is ___ the east of China.
He spoke so slowly that we all could ___ him.
I ___in North China, but now I ___ the weather in South China.