layer of rods and cones

例句：

1. 1. The cake has a layer of chocolate frosting on top.
   蛋糕顶层有一层巧克力霜。
2. 2. The book is divided into several layers of information.
   这本书被分成了几个信息层次。
3. 3. The scientist used different layers of materials to build the structure.
   科学家使用不同层次的材料来建造这个结构。