Concept:A nursery is a protected area where young plants are raised before transplanting to the main field.
Explanation:Some crops are not sown directly in the field because their seeds need special care during early growth.
Rubber is propagated from seeds that are first planted in a nursery.
The rubber seedlings are kept in the nursery and watered regularly.
After about 6 months, when the seedlings are strong enough, they are transplanted to the plantation field.
Cotton seed and soya bean are usually sown directly in the field.
Yam is planted using tubers or yam sets, not through a nursery.
Therefore, among the options, only rubber requires a nursery for seedling production.
Answer:A. Rubber