Instruction: Determine which of the given assumptions are implicit in the statement, then select the appropriate option.

Statement: The Andes mountains obstruct moisture-laden Pacific winds from crossing into the western plateau, resulting in arid conditions throughout the rain shadow zone.

Assumptions:
I. High mountain ranges can block moisture-bearing winds from passing into adjacent regions.
II. Areas positioned in a mountain range's rain shadow experience minimal precipitation.
III. Pacific winds are the only source of precipitation for the entire continent.

Correct Answer: Only I and II are implicit

Explanation:
An assumption is an unstated premise or underlying fact that must be assumed true for the statement to hold logically. Let us analyze each assumption individually based on the given statement:

1. Analysis of Assumption I:
The statement specifies that the Andes mountains obstruct moisture-laden Pacific winds from crossing into the western plateau. This specific real-world scenario relies on the broader factual premise that high mountain ranges are capable of blocking moisture-bearing winds from moving into adjacent regions. Therefore, Assumption I is implicit.

2. Analysis of Assumption II:
The statement notes that the obstruction of moisture-laden winds results in "arid conditions throughout the rain shadow zone." Since "arid" means extremely dry with very low rainfall, the statement directly assumes that areas located within a rain shadow experience minimal precipitation. Therefore, Assumption II is implicit.

3. Analysis of Assumption III:
The statement focuses only on how Pacific winds affect the western plateau and its rain shadow zone. It makes no broad generalization or claim about the weather systems of the entire continent, nor does it state that Pacific winds are the single, exclusive source of precipitation continent-wide. Therefore, Assumption III is not implicit.

Conclusion:
Since only assumptions I and II are necessary underlying premises for the statement, the correct option is Only I and II are implicit.