"The" is used before the names of specific rivers. Therefore, "the Yamuna river" is correct.

Understanding Articles in English
When discussing articles in English grammar, it’s essential to understand their function and usage. Articles help specify the noun they precede. In your example, the correct answer is "the" for specific reference.
Why "The" is Correct
- Specific Reference: "The Yamuna River" refers to a specific river known to both the speaker and listener. Using "the" indicates that you are talking about that particular river.
- Proper Noun: "Yamuna" is a proper noun, and when naming a specific river, we typically use the definite article "the" to denote its uniqueness.
Why Other Options are Incorrect
- Option A: "An"
- "An" is an indefinite article used before words starting with a vowel sound. It would imply any river, not a specific one.
- Option C: "Zero Article"
- The zero article means no article is used. This is incorrect here because "Yamuna River" needs a definite article to indicate it is a specific entity.
- Option D: "A"
- "A" is also an indefinite article, suggesting any river. It cannot denote the specific Yamuna River.
Conclusion
In summary, the correct article to use in your sentence is "the." It accurately represents the specific river being discussed, thus providing clarity and precision in communication. Using the correct article enhances the quality of your writing, making it more effective and understandable.