After you have insert RAYTRACE in the reflection map you will see that the materialeditor is showing new Settings.
当你为反射贴图通道添加了光线追踪贴图后，你会发现材质编辑器显示出新的设置。
3
Shows which material is currently assigned to it. Click on the button to get to the materialeditor where you can change texture or select another material.