A Spear or a robot has the quality of technology only when it______.

A．is used both as a cultural and a physical object

B．serves different purposes equally well

C．is utilized by man

D．can be of use to both man and animal

氟牙症的临床表现，错误的是（）

A.一般发生在恒牙

B.氟牙症的釉质硬度增加

C.氟牙症常发生在同一时期萌出的同名牙上

D.釉质上有白垩色到褐色的斑块

E.机体对氟化物的感受性存在个体差异