Who is most stupid ?

• A is sawing the branch he is sitting on — he will fall.
• B is also sawing the branch he is sitting on — he will fall.
• D is sawing the branch C is sitting on, so C will fall — but D himself stays safe.
• C, however, is calmly sitting on the branch while someone else is cutting it and doesn’t even realize it.

So C is the only one who will fall because of someone else’s action and isn’t doing anything to stop it — making him the most clueless.