Step 1: Understanding the Question:
This question tests knowledge of silvicultural operations.
Step 2: Detailed Explanation:
Tending operations are practices that improve the growth of young trees.
Weeding (A): Removal of unwanted plants.
Thinning (B): Removal of some trees to reduce competition.
Cleaning (D): Removal of inferior trees.
Soil working (C): Soil cultivation is not a tending operation; it is a site preparation operation.
Thus, the correct answer is soil working.
Step 3: Final Answer:
Thus, soil working is NOT a tending operation, which corresponds to option (C).
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