一艘轮船顺水航行的速度是20海里/小时，逆水航行的速度是16海里/小时，则水流的速度是______海里/小时．

According to INCOTERMS 2010, what is the trade term when the seller doesn’t undertake to pay for the cost of transport of the goods to a specified destination（ ）

A．FOB

B．CFR

C．CIP

D．CIF