In the sentence "Economically, we understand the world round us in terms of scarcity", which part contains the grammatical error?

Introduction / Context:
This is an error spotting question related to the use of prepositions and common phrases. The sentence attempts to describe how we see the world in economic terms. It is divided into three numbered parts and a No error option. Your goal is to identify which part contains incorrect or non standard wording, focusing particularly on prepositional usage around the phrase world round us.

Given Data / Assumptions:

• Part 1: Economically, we
• Part 2: understand the world
• Part 3: round us in terms of scarcity.
• Part 4: No Error.
• The intended phrase is likely the world around us, a common English expression.

Concept / Approach:
The adverb round can sometimes be used as a variant of around in informal British English. However, in a formal written context, especially in exam English, the standard phrase is the world around us. The rest of the sentence is grammatically sound: Economically is correctly placed as a sentence adverb, and understand the world in terms of scarcity is a proper clause. Therefore, part 3 is the one that must be corrected from round us to around us to fit standard formal usage.

Step-by-Step Solution:
Step 1: Examine part 1 Economically, we and see that it introduces a viewpoint and is grammatically correct.Step 2: Examine part 2 understand the world; subject and object are correctly structured.Step 3: Examine part 3 round us in terms of scarcity and identify the phrase world round us as slightly informal and non standard for exam purposes.Step 4: Replace round with around to get the world around us in terms of scarcity, which is the typical formal expression.Step 5: Conclude that the error lies in part 3.

Verification / Alternative check:
If we correct the sentence, it becomes: Economically, we understand the world around us in terms of scarcity. This is a smooth, coherent statement about economic thinking and fits well in formal essays. Keeping round us may be acceptable in casual speech but appears inconsistent with the exam style, which favours standard expressions. Parts 1 and 2 do not contain any issues with subject verb agreement or word choice, and part 4 cannot be correct because we do find a clear, conventional correction for part 3.

Why Other Options Are Wrong:
Part 1 uses Economically as an adverb correctly, indicating that the perspective is economic. Part 2 understand the world is grammatically correct and uses the verb understand in the right form. Part 4 No Error would only be valid if none of the parts needed correction, which is not the case once we identify the awkward phrase round us in part 3. Therefore, the only part that must be changed is 3.

Common Pitfalls:
Some students may be unsure about the difference between round and around and may hesitate to mark part 3 as incorrect. Remember that around is the default preposition in standard modern English when you talk about the world around us, people around me, or things around the corner. Round is more often found in specific fixed phrases or as an adjective related to shape. In high stakes exams, it is safer to choose the more formal and common variant.

Final Answer:
The incorrect part is 3, where round should be replaced by around, so option C is correct.