Answer:
A). It reinforces the idea of the United Nations’ strength and power.
Step-by-step explanation:
Repetition is one of the most commonly employed persuasive techniques to convey the ideas more effectively and convince the audience to believe in those ideas propagated by the speaker. In the given excerpt from President Roosevelt's union address, the word 'strike' has been constantly repeated by the president to reinforce the idea of the United Nation's strength and power. He intended to persuade his audience to believe in the tenacity and capability of the UN. Thus, option A is the correct answer.