— Sorry, sir. If my bike doesn't _____, I won't be late for school again.

— What you say is hard to believe. This is the eighth time you have said so.

                                                                                                                           [ ]

A. work out

B. come across

C. put off

D. break down

下列哪项是牙周炎的特殊损害，也是区别于牙龈炎的主要特点（）。

A.牙齿松动

B.牙龈红肿

C.齿槽骨吸收

D.牙龈出血

E.牙周袋形成