-That's a strange tent! It looks like a ballon! - Oh that CAN'T/MUST be a tree tent! I've seen one of tghem on the internet.
MUST be
-I'd love to get a tree ten! Are they expensive? - They CAN'T/COULD be expensive - my uncle has got one, and he hasn't got much money.
CAN'T be expensive
-Is there a capsite hear here? - I am not sure..There MUST/MIGHT be one near the lake. I've seen some people cooking on open fire there.
MIGHT be