[最佳答案] 这要取决于具体的语境。 in the river,在河里,是指在河水中,如鱼、沉船等,尤其注意在河里游泳也是用in the river。 on the river,在河上,是指在水面上,如船只、水坝、漂浮物等。此外还可以指在河岸边上,如村庄、市镇等。 例句: ⒈There were several canoes on the river. 河上有几条独木舟。(船是在水面上行驶,介词用on) ⒉Some kids are swimming in the river. 有些孩子在河里游泳。(是在水中游泳,介词用in) ⒊Now I came back to the village,only to see rubbish floating on the river. 现在我回到了村庄里,不想却看到河面上漂着垃圾。(垃圾是漂浮在水面上,介词用on) ⒋The level of pollution in the river is falling. 河水的污染物水平在下降。(污染的是河水,介词用in) ⒌On the river lies a small town.. 河岸边上有个小镇。(小镇在河岸边,介词用on)