In the essay, the point is made that perhaps the environment of the children has already guided their preferences in toys before the experiment was conducted. given the choices below, what is the earliest age at which environment could potentially shape the preferences of a child?
a. at age 3 or 4, when children are dressed in gender-specific clothing
b. at age 5 or 6, when children are given genderspecific toys
c. in middle school, where there is pressure to participate in generation sports and activities
d. in high school, where there is pressure to date people with certain types of personalities

The kidney filters potentially toxic substances in the blood, and thus “clears” the blood of those substances. this clearance function is dependent upon and proportional to the diffusion gradient of the substance across filtering capillaries, i.e. if the concentration of the substance is doubled, twice as much will be cleared from each ml of blood that is filtered. suppose that the body produces a constant amount of a substance x per unit of time. the kidneys eliminate substance x at a rate directly proportional to the concentration of the substance and the volume of blood cleared each minute (c): elimination = c × [x], where [x] is the steady-state concentration of substance x. imagine an individual with an initial concentration of x equal to [x]0 who develops kidney disease. her baseline clearance c0 drops to one half of the original (½c0). what is the new steady state concentration of x? (for simplicity, assume that substance x is 100% filtered by the kidney).