I was doing a CAE (Certificate in Advanced English) sample paper and there you should choose the best fit for a gap:
It is hard to believe that salt is now such a cheap _____, because centuries ago it was a commercial equivalent of today's oil.
A provision B utility C material D commodity
I know that the correct answer is D, "commodity". It's clear for me, why "provision" and "utility" don't fit, because they both don't have an appropriate meaning.
I do understand, why commodity is right, but I couldn't understand why "material" is wrong or even less suitable. For example, "The poodle we bought was the cheapest dog in the shop". "Dog" is a generic term for "poodle". So why can't we use "material" in the same way here?
Usually in this test there is a specific reason why the other answers don't fit. Even though people who answered my question below kindly explained that "commodity" is the best option due to economic context, it is still not quite clear to me if "material" is wrong or just less suitable. Some natives say it is just less suitable and some say it is wrong, cause it lacks an appropriate meaning.