The correct answer is option D. Calcium.
Low bone density can be due to a lack of calcium thus requiring supplementation.
Motor Unit Summation<span> - the degree of contraction of a skeletal muscle is influenced by the number of </span>motor units<span> being stimulated (with a </span>motor unit<span> being a </span>motor<span>neuron plus all of the muscle fibers it innervates; see diagram below).</span>
FALSE : the presence of harmful substances in the earth’s atmosphere is called air pollution
