It was hard for him to learn English in a family, in which _____ of the parents spoke the language.

A．none

B．neither

C．both

D．each

单向免疫扩散试验中Mancini曲线中K值等于（c=抗原浓度，d=沉淀环直径，k=常数）（）

A.C/d

B.C/d²

C.C/logd

D.logC/d

E.logC/logd