The correct answer is: c) The number of crops grown on a plot in a year.
Cropping intensity is the number of crops grown on a given piece of land in a year. It is calculated by dividing the total area of land under cultivation by the total area of land available for cultivation. A high cropping intensity indicates that the land is being used efficiently, while a low cropping intensity indicates that the land is not being used efficiently.
Option a) is incorrect because it refers to the number of different crops grown, not the number of crops grown on a plot in a year.
Option b) is incorrect because it refers to the proportion of land used for cultivation, not the number of crops grown on a plot in a year.
Option d) is incorrect because it refers to the productivity per unit area, not the number of crops grown on a plot in a year.