Final answer:
The thermal energy of the ice remained the same, then decreased as the ice froze at a temperature of -4°C.
Step-by-step explanation:
The correct answer is D) Stayed the same, froze, decreased. When the boys sat on the ice, the thermal energy of the ice stayed the same as long as the temperature remained at -4°C. As the temperature continued to drop, the ice froze and its thermal energy decreased.