Final answer:
The BEST protection for an EMT's upper body during an extrication operation is a fireproof turnout coat.
Step-by-step explanation:
The BEST protection for an EMT's upper body during an extrication operation is a fireproof turnout coat, which is option A. A firefighting turnout coat is specifically designed to protect against heat, flames, and other hazards faced by emergency responders. It is made of fire-resistant materials such as Nomex, which can withstand high temperatures. Additionally, a turnout coat provides additional protective features such as reflective strips for visibility and pockets for carrying tools and equipment.