Blood flows down a vertical tube by gravity only. Solve the appropriate Navier-Stokes equations to find the velocity distribution vz(r) and compute the average velocity. The diameter of the tube is 10 mm. The density of blood is 1050 kg/m3 with a viscosity of 3.5 cP. Assume incompressible fluid. Assume steady and laminar flow. Average velocity= flow rate/ area. Required:
Derive a fluid-flow equation starting from the Navier-Stokes equation with cylindrical coordinates.

as we know our atmosphere or air have different levels. every level has other gasses, and every gas has another permeability. when the light comes from lower permeability to higher permeability, it changes its direction. so that means that when the light comes from the moon to the earth, it changes it's direction many more times. it basically means that the shape of the light part of the moon is changed on the earth.

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i think the answer is a and b

i wish you luck

at right angles to each other