Verification of truth — necessary attribute: An oasis always has what essential feature?

Introduction / Context:
“Oasis” is a geographic term for a fertile spot in a desert where water is found. The task is to identify the necessary attribute that must be present for the location to qualify as an oasis.

Given Data / Assumptions:

• We use the standard geographical definition: an oasis exists because of water emerging (e.g., spring, well, aquifer-fed area) enabling vegetation.
• Optional or culturally associated elements (caravans, camels) are not definitional.

Concept / Approach:
Test each option against the definition: Is it possible to have an oasis without that feature? Only “water” is indispensable. Sand, travelers, or camels may be absent; “sand” is common in deserts but not what constitutes the oasis itself.

Step-by-Step Solution:

Verification / Alternative check:
Remove water → fertility disappears → not an oasis. Remove camels/travelers/sand → can still remain an oasis if water persists.

Why Other Options Are Wrong:

• Travelers/Camels: Historical association, not definitional.
• Sand: Deserts vary (gravel/rock), and the “oasis” part is defined by water and vegetation.
• None of these: Incorrect because water is essential.

Common Pitfalls:

• Choosing “Sand” by associating oasis with sandy deserts; the key is water.

Final Answer:

Water