Kate is very ________. She likes to stay at home and read books.
A:funny
B:quiet
C:outgoing
D:serious
如图所示图象中属于交流电的有( )
如图所示,两根长度不同的细绳,一端固定于O点,另一端各系一个相同的小铁球,两小球恰好在同一水平面做圆周运动,则( )