"Have you run a [the] marathon," should absolutely be accepted, because Ukrainian verbs don't have a present perfect tense. The context could apply to this usage.
Also, there is no context that specifies whether to use a definite article " 'the' marathon" or indefinite article " 'a' marathon," so either choice should be accepted.
There is still one option that has not been included: "you ran a marathon" In your correct answers the past is established by using a past tense indicator rather than the past tense verb. When I used the past tense verb (as indicated in your hints) my answer was marked incorrect,. This indicates that there is an inconsistency between your dictionary and your answer key.