Welsh has no indefinite article, so this could be translated into English as any of:
- They want/need cauliflower(s)
- They want/need some cauliflower(s)
- They want/need a cauliflower - although strictly this should be a singular cauli - blodfresychen, but in general people do not always make that distinction with vegetables, etc as bought and consumed.
It could, as mentioned above. This sentence seems to have been deleted from the course now, so I cannot check the full list of accepted answers. It may take some time for it to actually vanish from the system..