Brightness is an attribute of visual perception in which a source appears to be radiating or reflecting light.In other words, brightness is the perception elicited by the luminance of a visual target. This is a subjective attribute/property of an object being observed and one of the color appearance parameters of color appearance models.
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2nd level- walking
3rd- weight training
4th- soccer
i think it's <em>a) insometric stretching</em>
hope this helps