Some people are worrying about the possibility ________ cellphones could be responsible for a range of illnesses, from rashes to brain tumors.
She didn't answer the phone.She ___ be asleep.
___ people gather there, talking about the film about Comrade Lei Feng.
I can't remember where I have put that book.Maybe they are ___ which one is not correct.
More than one student ___ that experiment.
The teacher together with his students ___ down at the desk and having a discussion in the classroom.