------ I'm sorry to interrupt you, Sir．May I ask you a favor?

------ yes, _____．

A．take it easy

B．go ahead

C．Don't mention it

D．you will make it

一抛物线以y轴为对称轴，且过

点及原点，一直线L经过

和

点，则直线L被抛物线截得的线段的长度为( )．