I'm thinking the same, I was marked wrong for checking this option.

It is correct. Please report it.

It's not a definite object. :)

Only 3rd-person objects are definite. So with engem, téged, minket/bennünket, and titeket/benneteket you still have to use indefinite conjugation.

I can't see the answers. :D

Some correct translations:

A fiű szeret téged.

A fiú szeret. (ambiguous)

A fiú szeret titeket. (plural)

A fiú szereti magát/önt/magukat/önöket. (formal, singular/plural)

A fiú szereti. (formal, singular & ambiguous)

Having gotten a multiple choice question, I can explain why both I saw are correct. The translations were: A fiú szeret téged and Téged szeret a fiú which are both grammatically correct, since the subject a fiú is in the nominative case and the object téged is in the accusative case. So the only difference is emphasis, kind of like the difference between It is the boy who loves you and you are (the one) loved by the boy

Your sentence means 'The boy loves'. You need some sort of indication of 'you'.