on a river,on the river,in the river的区别

on a river,on the river,in the river的区别 in the river与 on the river的区别 on the river?in the river? in the river和on the river有什么区别 船是用in the river 还是on the river on the river 请名师指导：in the river 与on the river区别, 是The ducks are swimming on the river 还是in the river?是There a 是there is a boat in the river还是there is a boat on the river the village is a on the river [英语]在河上钓鱼的人是on the river还是in the river? Is there a river on the farm