There is no such thing as a stupid question! We learn by asking questions.
We don't give answers on this forum only hints.
Consider the bonding in related allotropes of carbon, namely graphite and
the fullerenes (e.g., C60, C70). Review the bonding (MO description) in benzene.
The "dangling" C atom in nanotubes probably have their bonding requirements satisfied
by the formation of C≡C bonds, but that is just a guess.