The answer is letter C.
We have boasted the protection of Great Britain, without considering, that her motive was interest not attachment; that she did not protect us from our enemies on our account, but from her enemies on her own account, from those who had no quarrel with us on any other account, and who will always be our enemies on the same account.
In this sentence, it is admitted that Great Britain protected the colonies, which would be for the gain of the colonies, but also that is did so for its own gain, so the gain was on both parts, "mutual" - I think that this is the correct answer.
They learn that Maggie is a true reflection of the human condition
The sentence <em>The findings of the study will be published in Scientific Journal next month</em> is in the passive voice because the subject of the sentence (<em>the findings of the study</em>) doesn't act but it is rather the passive recipient of the action. If we wanted to rewrite the sentence in the active voice, that would be:
<em>They will publish the findings of the study in Scientific Journal next month. </em>
<u>So, the correct answer is:</u> This sentence can be rewritten in the active voice.