电疗法基础知识中，“两种不同频率的交流电互相重叠时，合成后的电流的幅度变化”属于（）

A.电容

B.差拍

C.等幅振荡电流

D.减幅振荡电流

E.脉冲等幅振荡电流

—When were you born, Lily?

—I was born _______ July 18, 1990. [ ]

A. in

B. on

C. at

D. to