Our parents have done a lot for us. I think we should ______ them by working hard.

With the development of the central and western China，more and more modem cities have ——in what was a wasteland ten years ago 

The lecture was so complex that I simply couldn’t ______ at all. Could you explain it to me?

She said she could not _____ all the information given in the broadcast.

All the passengers were ______ of the flight which was put off because of heavy fog.