An exporter sells goods to a customer abroad on CIF and FCA terms. Who is responsible for the freight charges respectively （ ）

A．seller, seller

B．seller, buyer

C．buyer, seller

D．buyer, buyer

串级调节系统参数整定步骤应该为（）。

A. 先主环，后副环

B. 先副环，后主 环

C. 只整定副环

D. 没有先后顺序