Concept:Damping off is a fungal seedling disease favoured by overcrowding and excess moisture.
Explanation:Thinning removes extra seedlings from the seedbed or nursery.
This reduces overcrowding and improves air circulation around young tomato plants.
Better airflow lowers humidity and keeps the soil surface drier.
These conditions help prevent the spread of damping off disease.
Staking supports growing plants, while supplying means watering or adding nutrients.
Pruning removes unwanted branches, not seedlings.
Therefore, thinning is the most suitable control measure at the seedling stage.
Answer:C. thinning