当别人对你说：＂Sit down, please. (请坐)＂时，你应该说 ____________.

I________football when l was a child．

Though the teacher had explained it three times, many students still felt ____. It was so difficult a physics problem.[ ]

We ________ certain living things as birds not because they have long legs or short legs, but because they all have feathers.[ ]

Can you finish the work betterwith ______ money and _____ people