Cardiac output is affected by heart rate exercise stroke volume all of the above

Well if you are talking about cardiac output in terms of physical activity then the correct answer is all of the above. Heart rate, exercise, and stroke volume are all factors that can contribute to cardiac output---the volume of blood that is pumped by the heart per minute. The stronger your heart is the higher your cardiac output and the less the heart needs to beat and exert effort to provide you with the enough oxygen and energy you need.

The freezing point of the ice is lowered because of the rock salt which then allows the ice to observe heat from the ice cream mixture without it melting.