Answer:
I'd say your answer is D) Headache.
Explanation:
A headache isn't really visible and can't necessarily be measured, whereas all the other answer choices are both visible and can be measured in some way, shape, or form.
Most likely headache.
Jaundice can be seen from the yellowness from the skin, and if a person has fatigue.
Cyanosis can be seen from the bluish/greenish hue on a person's skin.
And heavy breathing can just be heard.
