A, Uhm
When you're so smart you know the answer but you're too lazy to say it. Or when you're too dumb to know the answer and you just make noise.
A: What's 2+2? B: Uhm... I don't know. I just like making noise.
A: What's your name? B: Uhm... I don't know, but I'm smart.
A: What's the capital of France? B: Uhm... I just like making noise.