Some verbs, some consisting of a noun and auxiliary する, work as both transitive and intransitive verbs, and 確定する is one such verb. It is used intransitively in your example with 無罪 being its subject. If there is no intransitive equivalent in English, the idea expressed by such a verb needs to be translated with a transitive verb either in the passive voice ...
That ような sounds redundant to me. It’s like saying:
It seems there are boys like those who will mistakenly think she likes them
Without it, the meaning basically remains the same.
It seems there are boys who will mistakenly think she likes them
A simple answer is, yes it is used as お返しする since the speaker is a child. It looks like the girl speaks without です/ます endings, and that is why お返しする is used.
Probably a confusing thing is that お返し is certainly お＋返し, but to mean the favor in return, お返し is the only possible form.
You can see many samples mentioned in the definition of 返し are prefixed by お, ...
言ったのは少女のひとりだ is also a valid sentence. It is understood as a statement of a fact about a past event. 言ったのは少女のひとりだった means the same but it somewhat sounds like it is describing the time when that event happened.
This is partially related.
A similar question could be asked about the tense of a cleft sentence in English. I found this but it is closed as “too ...
In the most prototypical usage, the verb かかる takes two arguments.
[activity/goal] に [time]（が）かかる
As an example, 避難に時間がかかる matches this pattern. 避難までに時間がかかる is the result of substituting the [activity/goal] part with a specific point of time that marks some event. In this particular example, it could be understood as either the beginning or the completion ...
Natural languages aren't like programming languages — due to ambiguity, a given word does not have the same "precedence" or "binding strength" in all contexts, thereby admitting multiple interpretations. Look at https://en.wikipedia.org/wiki/Garden-path_sentence for examples of this.
Programming languages are constructed to avoid this ...
耳の大きい in isolation is not a valid sentence, but it is correct as a relative clause with ga-no conversion applied. For example, the following sentences are correct.
I saw an elephant whose ears are big.
Here, 耳が大きい and 耳の大きい are modifying ゾウ as a relative clause, in which case が and の are (usually) interchangeable.
For 耳の大きい to ...