什么时候是look up them ,什么时候look them up?

look them up还是look it up 高中英语题look them up 和look up them 有什么区别,还是有一个是错的?我听说什么句子里用代词和用 look it up与look them up有什么区别,怎么用 翻译：pull your covers up and make them look neat look them 中间是? look them _____of them has a dictionary and____one of them can look up 是look after them,还是look them after? 是cheer them up还是cheer up them look up和look Dogs,especially,look up to their owners,which makes them fee ——of them has a dictionary so ____ one can look up words in