how to get the skybox-mesh.egg and urban-level-02-medium.egg

[jadyntao]

Hi,I run the file step_quad.py and then show the error as:
loader(error): Couldn't load file skyboxes/01-clean-day/skybox-mesh.egg: not found on model path (currently: "/g/MyCodes/citysim3d-master/examples;/e/Tools/Anaconda3/Anaconda3/envs/gymlab/Lib/site-packages/panda3d/etc/..;/e/Tools/Anaconda3/Anaconda3/envs/gymlab/Lib/site-packages/panda3d/etc/../models")
:loader(error): Couldn't load file levels/urban-level-02-medium.egg:not found on model path (currently: "/g/MyCodes/citysim3d-master/examples;/e/Tools/Anaconda3/Anaconda3/envs/gymlab/Lib/site-packages/panda3d/etc/..;/e/Tools/Anaconda3/Anaconda3/envs/gymlab/Lib/site-packages/panda3d/etc/../models")

Those files are in models.mf? If yes,how can I use them?