Final answer:
The disparity in rainfall across South America is largely due to the Andes Mountains causing a rain shadow effect, with moisture-laden winds from the Pacific Ocean precipitating on the western slopes and leaving the eastern regions dry.Option A is the correct answer.
Step-by-step explanation:
The eastern side of South America is wet, and the western side is dry primarily due to the rain shadow effect caused by the Andes Mountains. When moisture-laden air masses move from the Pacific Ocean toward the continent, they encounter the Andes. The air ascends the mountains, cools, and precipitates its moisture on the western slopes, which leads to high precipitation in places like southern Chile; however, as the air crosses over to the eastern side, it becomes dry, creating arid conditions in regions such as Patagonia and the Atacama Desert.
This phenomenon is also observed in other mountainous regions like the Southern Alps in New Zealand, the Himalayas, and the North American Cascades, where the windward side gets ample rainfall, and the leeward side experiences semi-arid to desert conditions.
Option (a) The Andes Mountains block the moisture-laden air masses from the Pacific Ocean is the correct option in the final answer because it specifically refers to the geographical feature that causes the disparity in rainfall between the eastern and western sides of South America due to the rain shadow effect.