Classification – Natural landforms vs man-made structure: three are natural features; one is an artificial structure. Identify the odd one out. Options: Valley, Sea, Tower, Mountain.

Introduction / Context:
Geographic classifications commonly distinguish natural landforms from human-built structures. That contrast establishes a straightforward outlier.

Given Data / Assumptions:

• Valley: natural low area between hills or mountains.
• Sea: large natural body of salt water.
• Mountain: natural elevated landform.
• Tower: tall man-made structure.

Concept / Approach:
Separate items by origin: natural vs artificial.

Step-by-Step Solution:
Valley/Sea/Mountain → natural landforms.Tower → man-made structure.Hence, Tower is the odd one out.

Verification / Alternative check:
Any encyclopedic list of landforms excludes towers, which appear in architecture/engineering references.

Why Other Options Are Wrong:
Valley/Sea/Mountain: All are generated by natural processes.

Common Pitfalls:
Confusing “sea” with “ocean”; both remain natural water bodies, unlike a tower.

Final Answer:
Tower