Answer:
The sentence from the story that best supports the idea that the event was of national importance is Papa glanced over toward the crowd. "Why that’s President Arthur himself!" he exclaimed.
Explanation:
It is well known that not all the events throughout the country are going to have the presence of the President, then when in the story "Behold the Brooklyn Bridge" it is mention by the character with total surprise that the President is in the place for the event, he gives it the level of national importance since it was part of the President's agenda.
A verbal strategy because it would show the point you are trying to get across
