All of us had a good time at Tom's  birthday party. [ ]

A. help each other    

B. enjoy ourselves

C. have a big dinner  

D. had a wonderful

每次治疗开始前和结束后及时踩脚闸（），减少回吸污染；有条件可配备管腔防回吸装置或使用防回吸牙科手机。