The real reason for the fire _______ a burning cigarette end.

3.     He is teaching in his hometown now, but he________ in a hospital for 10 years. 

Though we don’t know what was discussed, yet we can feel the topic_____.

Teenagers _____their health because they play computer games too much.

--- An ant has two stomachs --- one for itself, one for others.--- Really? Quite interesting. I ____ anything about it.