期前收缩的产生机制包括（）
A.附加的房室传导束
B.迷走神经张力增高
C.折返激动
D.触发活动
E.异位起搏点的兴奋性增高
参考答案：C, D, E
下列关予破产财产分配的清偿顺序，说法正确的是（）。 ①普通破产债权 ②破产人所欠职工的工资和医疗、伤残补助、抚恤费用 ③破产人欠缴的税款 ④破产费用和共益债务
A．①→②→③→④
B．④→②→③→①
C．②→①→③→④
D．②→③→①→④
Construction of the gigantic office building in this city was for years intermittent.
A．stopping and starting at intervals
B．something that will happen soon
C．being watched with keen interest
D．anything that comes and goes
