当动脉瓣关闭时,心脏内的血流方向是( )
如图是某电热水壶加热和保温电路原理图,R1=44Ω,R2=440Ω,当开关S1断开,S2闭合,电热水壶处于____ 状态;该电热水壶的加热功率是____ W.
—What does Anna look like?
—__________.