Answer:
A.Blood volume decreases
Step-by-step explanation:
Blood volume refers to the fluid substances including blood circulating in the body via blood vessels. The blood volume must be optimal in order to ensure that every organ in the body gets an ample amount of blood. One of the things that can result in alteration of the normal blood volume is DEHYDRATION, which is the loss of water from the body.
Dehydration decreases the blood volume because the water content in the blood becomes decreased as water is lost, which would have detrimental effects on the body because the blood pressure (force at which blood flows) will be reduced.
This is the case of the student in this question that loses a significant amount of water as sweat when he undergoes exercise in a hot weather condition. The loss of water will result in the decrement of his blood volume.