极化指数PI为R10min/R1min，当绝缘受潮或污染时，接近于（）
A、1
B、1.3
C、1.5
D、＜1
参考答案：A
不透明的袋子中有五个球，三红二白，从中摸一个球，记下颜色，放回去再摸一个球，则摸到二红的机会是______．
When the seller pays for all charges up to an including the loading of a consignment on board the carrying vessel, the term is （）.
A．DDU
B．FCA
C．FOB
D．CIF
