In this analogy based on water bodies, River is related to Stream as Ocean is related to which of the following: River : Stream :: Ocean : ?

Introduction / Context:
This question tests your understanding of the relationship between natural water bodies. The pair River : Stream shows a relationship between a larger body of flowing water and a smaller or similar type of watercourse. You must find the option that plays a similar role or shows a similar relationship with Ocean. Recognising such hierarchical or size based relationships is common in verbal reasoning.

Given Data / Assumptions:

• A river is a large natural stream of water flowing in a channel.
• A stream is a smaller or narrower body of flowing water similar in nature to a river.
• An ocean is a vast body of salt water that covers a major part of the Earth.
• The options include Current, Pond, Dam and Sea, which are all related in some way to water.

Concept / Approach:
The relation River : Stream can be described as "larger watercourse : smaller similar watercourse." We must identify the term that stands to Ocean in the same way that Stream stands to River. Among the options, Sea is a large body of salt water that is typically smaller than an ocean but of the same general type. Therefore, Sea is to Ocean as Stream is to River.

Step-by-Step Solution:
Step 1: Understand that a river is a substantial flowing body of water, while a stream is like a smaller version of a river.Step 2: Express the pattern as "larger water body of a kind : smaller similar water body."Step 3: Consider an ocean as an extremely large body of salt water that covers huge areas of the globe.Step 4: Look for a smaller but similar body of water among the options. Sea is a large body of salt water, but smaller than an ocean and often partly enclosed by land, so it fits this pattern well.Step 5: Evaluate other options. Current is a movement of water within a larger water body, not a separate body. Pond is usually a small still body of freshwater, which differs from ocean in type and scale. Dam is a human made structure that blocks water flow.Step 6: Conclude that Ocean : Sea mirrors River : Stream in a natural and meaningful way.

Verification / Alternative check:
We can test the analogy by converting it into words: "A stream is a smaller version of a river, just as a sea is a smaller version of an ocean." This statement is accurate in general geographic terms. None of the other options give a similarly clear and parallel description, which confirms that Sea is the correct choice.

Why Other Options Are Wrong:
Option A, Current, is only a flow within a water body and not itself a classification of water body. Option B, Pond, is small and fresh water, which does not correspond well with a huge salt water ocean. Option C, Dam, is a structure, not a natural body of water at all. They therefore fail to represent a smaller similar water body in relation to an ocean.

Common Pitfalls:
Some candidates may rush and choose Pond because it is a smaller water body, ignoring differences in type and context. Others might confuse terms like current and sea due to loose everyday usage. Always focus on what kind of entity each word represents and whether it truly mirrors the relationship in the example pair.

Final Answer:
The correct completion of the analogy is Sea, so option D is correct.