是Look,there are some books on he bookcase还是Look,there are some books in he bookcase

in the bookcase.
书架是有空间的.要用IN.Look,there are some toys on the bookcase还是Look,there are some books on the bookcase这个要根据语境了。On the bookcase是在书架的顶上面in the bookcase是 在书架上（就是书架里面）那这个呢，玩具就在书架上面Look,there are some toys on the bookcase.可以用。