动铁式弧焊变压器当手柄顺时针旋转铁心向里移动时电流减小。( )
参考答案:对
—_____ in summer here?
—It's not very hot. [ ]
A. What's the weather
B. What's that
C. Where's the weather
D. How's the weather
简述关键事件法的定义及优缺点。