The correct answer is C. Because we participate in the alliance system, our allies will come to our defense, and our invaders will soon regret their aggression.
Step-by-step explanation:
The word Logos refers to a mode of persuasion based on the appealing to the logic in order to convince the audience about something mainly by providing evidence such as facts or statistics that show the words of the speaker are true. This means the Logos relies on facts and evidence that support the speaker's ideas. In the excerpt presented the author is speaking about the national security and the attacks by another nation, suggesting to the audience it is necessary to take action to stop the other country's attacks. This implies the appeal to logos that completes the speech needs to show through facts and evidence the way action is necessary or how the attacks can be stopped.
Considering this, the most appropriate addition that completes the excerpt and uses logos is "Because we participate in the alliance system, our allies will come to our defense, and our invaders will soon regret their aggression" as in this excerpt the author is using a fact which is the alliance system (appeal to logos) and the excerpt is directly connected to the topic of the speech as the author explains the way the attacks will be stopped.