He has _______good knowledge of_____English language but not much of English history.

E-mail, as well as telephones, ___ an important part in daily communication

It is difficult for us to learn a lesson inlife_________we’ve actually had that lesson.

We have _________ homework today. Wedon’t have any time to watch TV.

geles Times reported that researchers may have found a way to ______ human life by changing certain genes, so that humans might expect to live twice as long.