在雷雨天不要走近高压电杆、铁塔、避雷针，远离至少（）以外。
A、10m
B、15m
C、20m
D、30m
参考答案：C
为什么变压器只能改变交流电，而不能改变直流电？
A portfolio manager is constructing a new equity portfolio consisting of a large number of domestic stocks. As the number of stocks in the portfolio increases, what happens to the systematic and unsystematic risk Systematic RiskUnsystematic Risk（）
A. Increases Remains the same
B. Remains the same Decreases
C. Remains the same Increases
