The phrase that best supports the answer to Part A (the theme of the text) is:
A. "After raging for a period of three days, fought desperately, in the face of its tremendous advantage, it subsided when it had reduced hundreds of blocks of valuable property to ashes and rendered over 250,000 people homeless." (Paragraph 19)
This phrase highlights the destructive power and devastation caused by the fire, emphasizing the theme of the text, which is likely focused on the catastrophic impact of the fire on the city and its residents.