Leketa is a secret agent. She needs to send secret messages to her partner, Daniel. Leketa uses the sound waves from the beat of a drum to send her messages. Leketa and Daniel create a secret code using a pattern of drum beats to communicate with one another. In which of the following places would using a drum work to send her secret messages? A. The drum will work on Earth, under the water, and in outer space.
B. The drum will work on Earth and under the water. The drum will not work in outer space.
C. The drum will work on Earth and in outer space. The drum will not work under the water.
D. The drum will work under the water and in outer space. The drum will not work on Earth.

Why did you choose your answer to Question 4? Explain in terms of sound waves.

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).