Mike:You look a bit dull today.______？Susan:I have some bad news. I got fired.Mike: Oh,no!

Mike:You look a bit dull today.______？Susan:I have some bad news. I got fired.Mike: Oh,no! You must be kidding. How come？Susan:Its a long story.

A．What"s up

B．What"s on

C．What then

D．What of it

请帮忙给出正确答案和分析，谢谢！