It is uncertain ______ side effects these weight-loss drugs will bring about, although hundreds of thousands of patients have taken it.
The scientists are studying the effects of human activities______the environment.
The law about banning using thin plastic bags came into_____from 1st Jane this year.
I have offered to work for the store owner _____ one night’s stay.
Tom said he had been working for three hours, _____ ,evidently, was untrue.
---May I use your cellphone?---_____. We are good freinds