Which of these statements is the best reason for countries to work together to address environmental issues? a. international treaties are largely ineffective because developing countries lack the resources to enforce them. b. pollution made in one country might contaminate the ground, water, and air of other countries c. pollution made in one country trends to stay in that country and harm only that country's residents d. environmental damage is caused mainly by developing countries that need to work together.

6/12=1/2

step-by-step explanation:

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.