Explanation:

The correct answer is option 'A', which states that the rainless nature of the Chilean and Peruvian coasts is due to the presence of a cold ocean current along the coasts.

Presence of Cold Ocean Current:
The Pacific Ocean off the coasts of Chile and Peru is influenced by the Humboldt Current, also known as the Peru Current. This current is a cold oceanic current that flows northward along the western coast of South America. It originates in the Southern Ocean and is driven by the South Pacific Gyre. The Humboldt Current is characterized by its low temperatures and high nutrient content.

Effect on Rainfall:
The presence of the Humboldt Current has a significant impact on the climate of the Chilean and Peruvian coasts. The cold ocean current helps to create a stable atmospheric condition known as a temperature inversion. This inversion layer prevents the formation of clouds and the vertical movement of air, leading to a lack of rainfall.

Temperature Inversion:
Temperature inversion refers to a change in the temperature profile of the atmosphere, where the temperature increases with altitude instead of decreasing. In the case of the Chilean and Peruvian coasts, the cold water of the Humboldt Current cools the air above it. This cold air is denser than the warm air above it, creating a stable layer that prevents the upward movement of warm air and the formation of clouds.

Lack of Rainfall:
As a result of the temperature inversion caused by the cold ocean current, the Chilean and Peruvian coasts experience very little rainfall. The stable atmospheric conditions prevent the lifting of warm, moist air, which is necessary for the formation of clouds and precipitation. This rainless climate has led to the development of deserts along the coasts, such as the Atacama Desert in Chile and the Sechura Desert in Peru.

Conclusion:
In conclusion, the rainless nature of the Chilean and Peruvian coasts can be attributed to the presence of the Humboldt Current, a cold ocean current that creates stable atmospheric conditions, preventing the formation of clouds and rainfall.