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。