in the rivers 还是 in the river on the hill 还是 on the hills 什么

on hills还是in the hills 在山上用in还是on野餐用on the hills 还是 in the hills 是in the hill还是on the hill 船是用in the river 还是on the river 在丘陵上的英语翻译,是on the hills还是in the hills on the river?in the river? 是The ducks are swimming on the river 还是in the river?是There a in the river和on the river有什么区别 in the newspaper 还是on in还是on the newspaper in还是on the blackboard in the town还是on