The ration between crop ET and Pan ET, where the crop is raised on a large scale under optimum growing condition is called

Answer: Option B

Crop evapotranspiration represents soil evaporation and the water used by a crop for growth and cooling purposes.
The ratio between crop ET and Pan ET, where the crop is raised on a large scale under optimum growing conditions is called crop coefficient.
Potential evapotranspiration is the evaporation and transpiration that potentially could occur if a field of the crop had an ideal unlimited water supply.