From the perspective of grammatical structure, because there is than behind it, the answer should be C, because ABD's three answers are not comparative.

There is no grammatical error in the answer itself, but it is not appropriate here. As concrete work and works, works are countable. Your teacher is right.

B Answer: Did you dial the wrong number? Is this a very interesting job? If you enter this, it is grammatically wrong.

C answer, comparative, can be used in several languages, so it can be used. It can be a profession for a football player to become a football player.

D answer, grammatical error.

There is another problem of the same type. My job is to feed pigs, but I think it is better than other jobs. The answer is a much more interesting job, not a more interesting job, but a very interesting job.