I'm going to spend the winter vacation in Shanghai,_______I have relatives.

A．which

B．that

C．where

D．when

牙髓失活法最严重的并发症是

A．封药后疼痛

B．失活剂烧伤

C．急性牙髓炎

D．急性根尖炎

E．急性龈 * * 炎