Final answer:
Reagan considered the Challenger disaster significant enough to alter his State of the Union address to focus on mourning and remembrance. The correct answer is option C.
Step-by-step explanation:
From the opening statement of Reagan's speech, we can infer that he considers a recent event, which has resulted in mourning and remembrance, serious enough to change his planned speech on the state of the Union. Option C, that Reagan believes the Challenger disaster is an urgent matter, most closely aligns with the inference that can be made based upon the gravity of his words and his decision to shift the focus from a standard policy report to addressing this tragic event.