Water reaches its smallest density at approximately 4 degrees Celsius, where it is at its maximum density. Below and above this temperature, water's density decreases. However, the options provided do not include 4 degrees Celsius.
If we consider the temperatures provided, the answer that feels closest conceptually would be option D, 80 degrees Celsius, as it would correlate to a lower density than at 4 degrees Celsius, though it is not the absolute minimum density point.
So, I would suggest responding with D (80).