腐苔不具备的特点是( )。

A．浊而滑腻

B．刮之易脱

C．形如豆腐渣

D．苔质颗粒较大

E．松软而厚

The students have cleaned the classroom,_____?[ ]

A. so they     

B. don’t they    

C. have they    

D. haven’t they