—Did Jack come back early last night?

—Yes.It was not yet eight o'clock ______ he arrived home.[ ]

A. before  

B. when  

C. that  

D. until

二度Ⅱ型房室传导阻滞的心电图表现是()

A.在2：1阻滞时，易误认为房早未下传及窦性心动过缓

B.有心室夺获

C.常伴有3：1、4：1房室传导阻滞

D.P-R间距恒定

E.P-R间距常不恒定