特别感谢@无色之绿233 的发现：这关的地形正好只构建到视野边界（需要按住 D 键防止视野回弹），所以在边界处可以抓住球，运到下方。
Special thanks to @无色之绿 for his finding that terrains in this level happen to be placed right on the boundary of the view (you need to hold D key to keep the camera), so you can grab balls and move them below.
