Final answer:
The correct extinguishing agent for Class D fires is carbon dioxide as it displaces oxygen and cools the fire.
Step-by-step explanation:
The correct answer is d) Carbon dioxide. Class D fires involve combustible metals such as magnesium, titanium, and lithium. These fires require a specialized extinguishing agent that can withstand the high temperatures and react chemically with the burning metal to smother the fire. Carbon dioxide is commonly used as the extinguishing agent for Class D fires because it displaces oxygen and cools the fire, effectively suppressing it.