After a major disturbance in an ecosystem, succession can restore many of the original plants and animals that lived in the habitat before the change. Which of the following is an example of primary succession? A. After a wildfire in central Florida, black bears return to the forest.

B. After a volcano on a Hawaiian island, lichens grow on the cooled lava.

C. Trees begin to grow years after crops are not produced on a farm field.

D. Following Hurricane Matthew, tropical plants grew after flooding drained.

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).