Tom, clean up the broken glass _________ someone walks on it.
----_____I return the dictionary within three days?----No, you_____. You_____ it for five days.
Controlling water-pollution is necessary_____ it will be expensive.
Such a person _____ you talked about is seldom seen now.
_______ the teacher’s instruction in the lab_____ important.
E-mail, as well as telephones, ______ an important part in daily communication.