It's important a healthy lifestyle. [ ]
A. have
B. has
C. to have
D. having
答案:C
牙菌斑形成的最早阶段称为()。
A.获得性薄膜
B.釉护膜
C.细菌菌膜
D.唾液膜
E.透明膜
管电压的单位是()。
A.mA
B.mV
C.A
D.kV
E.dV