Write down a suitable word in meaning with the letter given.

1. very good—                   

2. not dirty—                   

3. at once—                   

4. be afraid of —                  

5. fewer than many but more than two—                  

牙髓塑化治疗时，拔髓的要求是（）。

A.保留根尖1/3处牙髓

B.尽量拔除牙髓

C.穿刺出根尖孔

D.可以不拔除牙髓

E.保留根尖1/2处牙髓