One of the very important documents in the foreign trade business is BL. B/L is the abbreviation for ______.

A．Bill of Lading
B．Commercial Invoice
C．Buying Contract
D．Letter of Credit

充电电路接线正常，但不能充电，不属于充电机故障的是（）。

A.电压低

B.晶闸管断

C.单结管坏

D.蓄电池断路