"This is not an apple, but a car."
Translation:Ez nem alma, hanem autó.
"Ez nem egy alma" is also correct. The article can be omitted in this case.
I haven't seen elol yet in this lesson except as a wrong option for this question and I'm not seeing a translation. How does it translate?
Elöl means in front: Elöl áll a legalacsonyabb fiú. -- The shortest boy stands in front.
Elől means away from: Elfut a kutya elől. -- He runs away from the dog. It also means from in front of, but I can't think of an example where the English translation doesn't sound weird.
hanem is sondern, de is aber :D
(hanem / sondern = "but rather, but instead")
The accepted translation misses the indefinite articles. This is okay, but I think it is safe to use include the indefinite articles too as long as you are learning the language... With experience and better understanding of hungarian you might know where you can drop those later on.