How can you take____ for granted that you can get something for nothing?

The old lady, ____ had been killed in the war, was given help by the local government.

After a long walk in the sun, they wanted to drink         .

______ the Chinese have been to Beijing.

 —Is there any vaccine(疫苗) against H1N1 flu that can be used on humans?—No, but scientists are working to develop ________ .