Joe won the first prize on Sunday and, tears rolling down his cheeks,           it a turning point for him. [      ]

A. called  

B. calling  

C. having called

D. to call

选择高压断路器应从（）方面因素考虑。

A、动稳定

B、热稳定

C、动作时间不必考虑

D、操作方式