— I'm thinking of the test tomorrow. I'm afraid I can't pass this time.

— ________! I'm sure you'll make it. [ ]

A. Go ahead      

B. Good luck

C. No problem  

D. Cheer up

可直接抑制牙菌斑的方法有（）

A.使用木糖醇

B.使用激光

C.使用核酸疫苗

D.替代疗法

E.牙膏加氟