VOZITI SE u Prošlom Vremenu

Voziti se is a reflexive verb, so every sentence in the past tense carries two little words at once: the auxiliary from biti and the reflexive se. They are both clitics, they both want second position, and they have a fixed order — auxiliary first, se second.

That highlighted row is the whole difficulty of this exercise. In the third person singular the auxiliary je is dropped when se is there: Jovan se vozio, never "Jovan se je vozio". Learners who know the rule for other verbs keep waiting for a je that is not coming — which is exactly why sentences 7 and 9 want se in the blank, not an auxiliary.

The other trap is word order. When the sentence starts with a question word or an adverb, the clitics still land in second position, so they jump in front of the subject: Kako su se ljudi vozili? and Kada su se oni vozili? — not "kako ljudi su se".

And watch the participle, because it agrees with the subject and not with the clitic: vozio for a man, vozila for a woman, vozili for a mixed or male group, vozila again for deca.