C. It highlights the critical obligation Ford will have in serving as the President, which conveys a concerned tone.
Explanation:
The highlighted phrase affects the tone of the speech by <em>highlighting the critical obligation Ford will have in serving as the President, which conveys a concerned tone.</em>
Actually, from the passage we discover that the speaker was referring to Ford who will be serving as the President. It reveals that the speaker feels concerned about the weight of responsibility and obligations that actually lies on the President. The speaker tends to empathize with the President as he shows to be aware of what lies ahead for him.
