Concept:Productivity means getting more output from the same level of inputs.Explanation:Technological change improves the efficiency of production.It allows firms to produce more goods and services without increasing inputs.This directly raises productivity.Using obsolete capital reduces efficiency and lowers productivity.Expanding land under cultivation or increasing the labour force raises total output, not productivity per unit of input.Therefore, technological change is the key factor that enhances productivity.Answer:B. Technological change.