Final answer:
When the witches' brooms are stolen, they ride on a variety of things, including a donkey, cars, and even as riders.
Step-by-step explanation:
The witches ride on different things when their brooms are stolen. In one passage, a boy comes riding by on a donkey, playing a flute. In another passage, the witches ride in a many-wheeled procession with countless cars escorting them. And in yet another passage, the witches ride in cars, while the speaker refers to them as 'riders'.