In the sentence "The first and decisive step in the expansion of Europe overseas was the conquest of Atlantic Ocean", which part contains the grammatical error?

Introduction / Context:
This is an error-spotting question that checks your understanding of correct article usage in English, especially with geographical names such as oceans and seas. The sentence describes a historical step in the expansion of Europe overseas and is divided into three numbered parts plus a No error option. Your task is to identify which part contains the grammatical or usage error.

Given Data / Assumptions:

• Part 1: The first and decisive step
• Part 2: in the expansion of Europe overseas
• Part 3: was the conquest of Atlantic Ocean.
• Part 4: No error.
• The noun phrase Atlantic Ocean is a proper geographical name.

Concept / Approach:
In standard English, when naming oceans and seas, we normally use the definite article the. For example, the Atlantic Ocean, the Indian Ocean, the Pacific Ocean, the Mediterranean Sea. In the given sentence, the phrase of Atlantic Ocean lacks the definite article and therefore sounds incomplete and ungrammatical. The rest of the sentence is structurally sound: the subject, verb, and prepositional phrases are correctly formed. Thus, the error is confined to part 3, where the article the is missing before Atlantic Ocean.

Step-by-Step Solution:
Step 1: Examine part 1: The first and decisive step. This phrase uses correct adjectives and article for step; there is no issue.Step 2: Examine part 2: in the expansion of Europe overseas. This prepositional phrase is grammatically correct and idiomatic.Step 3: Examine part 3: was the conquest of Atlantic Ocean. Here, the structure requires the conquest of the Atlantic Ocean.Step 4: Recall the rule: we normally say the Atlantic Ocean, not simply Atlantic Ocean, except in certain shortened headings or labels.Step 5: Conclude that part 3 contains the error because it omits the definite article the before Atlantic Ocean.

Verification / Alternative check:
If we correct part 3, the sentence becomes: The first and decisive step in the expansion of Europe overseas was the conquest of the Atlantic Ocean. This is a smooth and grammatically correct sentence. If we attempted to adjust any of the other parts, we would either break correct structures or lose the original meaning. The phrase expansion of Europe overseas is a standard historical expression, and the first and decisive step is a proper noun phrase. Therefore, the only correction needed is the insertion of the in part 3.

Why Other Options Are Wrong:
Option 1 contains a clear and correct noun phrase with appropriate adjectives. Option 2 is a balanced prepositional phrase with no article or preposition errors. Option 4, No error, cannot be correct because we have identified a specific and well known rule violation in part 3. Thus, options 1, 2, and 4 do not contain the error the examiner is testing.

Common Pitfalls:
Students sometimes overlook fixed rules about articles with geographical names, focusing instead on more complex grammar like tenses or subject verb agreement. Another common mistake is to suspect expansion of Europe overseas or first and decisive step because they sound more abstract. To avoid such pitfalls, remember that large water bodies like oceans and seas almost always take the article the in full sentences.

Final Answer:
The error lies in the phrase of Atlantic Ocean, which should be of the Atlantic Ocean, so the incorrect part is 3, making option C correct.