. From: Twitter

A. What are you ______ at?

B. Nothing.

A. Really? What's so funny, then?

B. What makes you think I was _______ at you?

A. You were looking right at me.

B. Was I?

A. Yes. So at what then?

B. The spider on your shirt!

A. Aah!

a. thinking

b. laughing

c. looking

d. staring

The answers are

b. laughing for the first and third statements

The reason is clear if we look at the third statement (a question): ”What's so funny?'

Culture:
Be careful. When a native-speaker asks "what's so funny?" be sure to look at his or her face. Does he or she look angry? 'What's so funny?' is not always a light, rhetorical question; it could be a challenge coming from his or her perception that you are laughing at him or her. If you hear, 'Ill give you something to laugh about', a fight could be coming.