---Are the Smiths living in the house alone ?--- Yes, although they have three sons, _____ of them live with their parents.

 You may depend on ____ that they are of much value.

No bread eaten by man is so sweet as ______earned by his own labour.

One of the students hasn’t prepared _____ lessons very well.

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