Part A
The main idea of "Queen of the Falls" is:
Annie is the first person to go over Niagara Falls in a barrel and live to tell about it.
Part B
The detail from the text that best supports the answer to Part A is:
“And I am content when I can say, ‘I am the one who did it.’”
This quote emphasizes Annie's achievement and the significance of her daring act of going over Niagara Falls in a barrel.