Step 1: The importance of mother tongue in learning.
Teaching in the mother tongue allows students to understand complex concepts more easily and clearly, as they are more familiar with the vocabulary and structure of their native language.
Step 2: Why other options may be less effective.
- (B) Teaching in a foreign language might hinder conceptual understanding, as students may struggle with comprehension.
- (C) Teaching in a regional language might be more effective than a foreign language but could still present challenges for students with limited proficiency.
- (D) National languages can vary in their effectiveness depending on the students' familiarity with the language.
Step 3: Conclusion.
Conceptual clarity is best achieved when teaching takes place in the mother tongue, as it enables easier understanding and communication.
Final Answer: Mother tongue.