Missing plugins in CitySample demo project, rendering it useless

I downloaded the CitySample project to learn but when I opened the project, it shows the following plugins are missing:

HoudiniEngine
Traffic
CitySampleMassCrowd
Hoverdrone
SoundScope
CitySampleSensorGrid

It then asks to continue loading, even it it may render some assets created with any of these are inaccessable.
If I say “No”, loading s aborted (obviously)
If I say “Yes” loading resumes but aborts, it cannot be loaded.

I tried to locate the plugins but none is found.
This information is omitted on the FAB site!!!