如图，△ABC 中，AC=BC，∠C=90度，AD平分∠CAB，DE⊥AB，若AB=20厘米，则△DEB的周长为         厘米。

—Are you guys ready for “The Campus Singers Competition”?

—Sure！Since we are young, try it, _____ we will regret!

A．and

B．but

C．or

D．then