变配电站远动设备在交流电消失后不间断电源维持供电时间应不小于(),无人值班厂站宜不小于30min。
A.20min
B.30min
C.50min
D.40min
参考答案:A
He says he really can’t _____ to wait another day. [ ]
A. waste
B. afford
C. spare
D. pay
目前公认引起先天性胆总管囊肿的主要原因()
A.肝内胆管闭锁
B.胆总管远端神经节细胞发育异常
C.胆胰管连接部异常
D.胆道上皮增生不平衡
E.病毒感染