Which statement about moisture variation and weather on compaction curves is true?

• A. The optimum moisture content is fixed and does not change with weather.
• B. Weather conditions have no impact on density after compaction.
• C. The moisture fluctuations can be ignored when planning compaction.
• D. Moisture fluctuations shift the optimum moisture content for maximum density; rain or drought can reduce achieved density and require adjustments.

Answer: (D)