Physiology Something that can obtain or provoke a physiological answer in a cell, a tissue, or an organism. A stimulus can be internal or external. Sense organs, such as the ear, and sensory receptors, such as those in the skin, are receptive to outside stimuli such as noise and touch. A stimulus can be external, indicating it happens outside the organism.
Oh the answer is the Mantle, You can look at a chart and easily find the answer if you don't believe me. But here is a reasoning; Magnesium as well as Aluminum are located within the Mantle.
