Concept:Derived demand means the demand for a resource or factor that depends on the demand for the final good it helps to produce.
Explanation:Labour is a factor of production, not a final product meant for direct consumption.
Its demand is derived because workers are needed only to produce other goods and services.
For example, the demand for steel creates a derived demand for steel workers.
If the demand for steel falls, the demand for steel workers also falls.
Textbooks, staple food, and mobile phones are final goods demanded for their own sake.
Therefore, labour is the correct example of derived demand among the given options.
Answer:B. labour