"Seu carro precisa de uma revisão."

[ka7th]

it should be check, not cheque and revision should be acceptable

[Gooselingo]

I was marked wrong for putting 'duma' when its a structure which I got taught very early on in Portuguese?

[Luis_Domingos]

"Duma" is not wrong per se, but it (de + indefinite article) probably the least common of all contractions (even in EP).

That said, please report any sentence where it is not allowed as an answer. Good luck with your studies :)