当三相电源为Y型链接时，线电压与相应相电压的关系为（）

IS0 14000是( )管理体系标准。

A．健康

B．安全

C．环境

D．健康、安全、环境

停炉过程中，总风量不得低于（）。

A、50％

B、20％

C、30％

Which of the following statements about duration is TRUE（）

A. The result of the formula for effective duration is for a 0.01% change in interest rates.

B. A bond’s percentage change in price and dollar change in price are both tied to the underlying price volatility.

C. The formula for effective duration is: (price when yields fall - price when yields rise)/(initial price × change in yield expressed as a decimal).