The number of the teacher invited _____ twelve, but a number of them ___ late for different reasons.

A．were; was

B．was; was

C．was; were

D．were; were

哪些是蓄电池的安装要求（）。

A.池工作时应平放，端子向上；放电池的台面应平整光滑无砂砾和尖锐物

B.电池放在容器中时，应留有呼吸孔

C.电池引出线端子及电池面应防溅水，并应防止落物造成短路。在出线端上不准使用烙铁焊接

D.电池应远离火源，避免太阳直晒、避免浸水结冰等情况