Concept:The law of diminishing returns applies to changes in a variable factor of production when other inputs remain fixed.
Explanation:In the short run, at least one factor, such as land or machinery, is fixed.
The producer keeps the fixed inputs constant and increases one variable factor, like labour.
Initially, total output rises at an increasing rate.
After a certain point, each additional unit of the variable factor adds less extra output.
This decline in marginal returns is the law of diminishing returns.
It operates only because some factors are fixed while others vary.
Thus, it is associated with variable factors, not with fixed inputs, plants, machinery, or equipment.
In the long run, all factors become variable, so this law is essentially a short-run phenomenon.
Answer:B. variable factors of production.