Exercises that improve cardiovascular fitness improve body composition, because they
a. increase body fat
b. increase body tissue
c. release energy
d. store energy

Exercises which improve cardiovascular fitness improvise the body compositions as they release energy. Hence, option C is correct.

Further Explanation:

Cardiovascular fitness refers to the ability of the lungs as well as heart to provide oxygen rich blood to the muscle tissues which are working. It also refers to the ability of the muscles to utilize the oxygen in order to generate the energy for the movement of the body. This kind of fitness is known to be health-associated element of physical fitness which is brought about through the physical activity. An individual's ability to supply oxygen to the muscles is mainly affected by many physiological parameters. These parameters include cardiac output, volume of stroke, heart rate, and maximal output consumption.

As the anaerobic or aerobic capacity elevates, general metabolism increases, haemoglobin elevates, muscle metabolism gets enhanced, buffers found in the bloodstream also elevates,, stroke volume gets better, and venous return also improves. In order to regulate the optimal delivery of oxygen to the working muscles, an individual would require to train or engage itself in activities which will accumulate the energy stores required for sport. This is known as metabolic training. This is segregated into aerobic and anaerobic.  Body composition also gets better because the energy is released which aids in improving the muscle strength and muscle endurance. Hence, option C is correct.

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Answer Details:

Grade: High school

Subject: Biology

Chapter: Health and exercises

Keywords:

Body composition, energy, energy stores, muscle strength, muscle endurance, metabolic training, cardiovascular fitness, exercise, aerobic, anaerobic, physical activity.

i think the answer is a.keratin is the pigment responsible for skin color.