---Did you notice someone enter the classroom just now?---Sorry, I didn’t. I _____ my lessons at that time.
Nanjing is one of _______ in China.
We are sure one day the air in Beijing will be much ______ than today.
We arrived _____ Shanghai______ the morning of July 2nd.
_____ too much TV isn’t good _____ our eyes.
The weather in Beijing is ________.