A:frightening; cried
B:frightening; crying
C:frightened; crying
D:frightened; to cry
He that he knew nothing about computer, so he began to work hard at it.
第二次工业革命的显著特点是( )
电阻器、电容器和电感器是电子设备中常用的电子元件。如图所示电路图中,符号“C”表示的元件是( )