The best explanation why the area between Spain and Gaul was not part of the Roman empire until that later period was a culmination from both undesireability and difficulty in accessing this region due to its mountaineous nature. So I would wager the answer being both C and D - undesireability and difficulty in access.
The second sentence sounds correct...
These students were forbidden to talk in their own languages, keep to their customs (such as keep their long hair, follow their religions, etc)
hope this helps
