－ _______does Nancy help the old lady with her housework－ About twice a week.

The plane _______ at 7：00 p.m.，so I have to be at the airport by 6：40 at the latest

Do you know why the Yellow River basin is called the Cradle of Chinese Civilization? —Well, well, _____I’ve never read about that

_____ in thought, he didn’t notice his teacher coming into the classroom at all [ ]

______ many times, he has already known how to do it.