Step 1: Understanding the Question:
This question tests knowledge of experimental designs and their suitability.
Step 2: Detailed Explanation:
Latin Square Design is used when there is variation in two directions (row and column).
It is used when the land has fertility gradients in two directions.
When treatments > 10 (A): LSD is not suitable (too many treatments).
When treatments < 3 (B): RBD is sufficient.
Highly undulated land (D): Not suitable for LSD.
Thus, the correct answer is if the land has variation in two directions.
Step 3: Final Answer:
Thus, LSD is used if the land has variation in two directions, which corresponds to option (C).
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