How does the digestive system help the muscular system? A.
The digestive system absorbs the nutrients necessary for the functioning of the muscular system.
B. The digestive system delivers the blood used by the muscular system.
C.
The digestive system exchanges gases used by the muscular system.
D. The digestive system provides structural support to the muscular system.

I would say the answer is A... but I'm not so sure

a coal burning power plant

speed of light in vacuum is 300,000 km/s

speed of light in other mediums is given by the expression v = c/n, where c is the speed of light in vacuum and n is the refractive index of medium.

for the first medium v = 200,000 km/s

  so, refractive index of medium = 300000/200000 = 1.5

    1.5 refractive index is usually for glass. so first medium is glass.

for the second medium v = 250,00 km/s

so, refractive index of medium = 300000/250000 = 1.2

    1.2 refractive index is usually for water. so second medium is water.

for the third medium v = 0 km/s

so, refractive index of medium = 300000/0 = ∞

    ∞ refractive index is usually for opaque mediums. so third medium is opaque medium.