The correct answer to the question "Which word suggests a topic of the speech?" is the second option: Duty.
The speech talks about a nation's duty towards righteousness and justice, not only when discussing political and public matters, but also personally, as a virtue all people must carry inside themselves. At the beginning of his speech, the speaker conveys a feeling of gratitude for all that was given to his people, when he says "with gratitude to the Giver of Good who has blessed us with the conditions which have enabled us to achieve so large a measure of well-being and of happiness". Then, the speaker calls attention to the fact that "Under such conditions it would be our own fault if we failed", meaning that his people should consider their responsibility any wrong actions they would be driven to take. As free and mighty people, he/she says that "a full acknowledgment of the responsibility which is ours" is necessary. When the speaker states that "We must show not only in our words, but in our deeds", he/she makes it clear that, as consequence of their well-being and success, they have the opportunity and the obligation to be right and just toward other nations. Therefore, the main topic of this speech would be the people's duty towards others, considering their privileged position.
The correct answer couldn't be the first option, "<em>Aggression</em>", because this word is only mentioned in the end, when the speaker says that "no strong power should ever be able to single us out as a subject for insolent aggression", as a result of their actions taken with justice, which takes the reader one more time to the main topic, the duty of righteousness toward others.
The correct answer couldn't be the third one, "<em>Peace</em>", because, although being at peace seems to be one of the speaker's objectives, he/she states that only by avoiding wrong deeds and always acting according to their duty to justice could the people reach and keep peace with other nations.
The correct answer couldn't be the fourth one, "<em>Realization</em>", because, even though the realization of the people's blessings could take them to feel like they are in a position to act right and help others, the main objective and topic of the speech are still fulfilling a duty.