1. The flat next door has been empty for 3 weeks.
Our neighbors must be in vacantion.
They might be in visit to some far kins.
They could be just dead, whatever.
2.There's smoke coming from that old building over them.
It must be a fire.
Someone might burn some cookies.
It could be a very large group of smokers there, a reunuion. :)
3.That's Russell over there, isn't it? I thought he'd gone on holiday.
He must be wrong.
He might changed his plans.
He could just wanted to avoid you. :))