8. became the primary commercial enterprise and were the primary means of commercial transport.

Corporation

Trucks

Explanation:

There are various methods of commercial enterprise. There can be sole proprietor, partnership arrangement, corporation and joint ventures. It is dependent on the requirements of a person who wishes to enter the business. The primary commercial enterprise is corporation. It is regulated by the government and fund is collected from the shareholders. The primary mean of commercial transport is trucks. They are used to move raw material and finished goods from factory to the stores.

pecialized keyboards

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.