甲、乙两电阻之比是3 :1,将它们串联后接入电路中,若测得乙电阻两端的电压为4V,那么这个电路的电源电压为:[ ]
A.4 V
B.8 V
C.12 V
D.16 V
D
流行性腮腺炎的肿胀部位为( )
A.颈前B.以耳垂为中心C.耳后D.面颊部E.颌下
I can see you have put a lot of time( ) it.
A.into
B.on
C.with
D.under