Conna wants to track the rate of growth of a seedling.
We have to find the appropriate unit for describing the rate in the given context.
Among these units,
millimeters per minute is not the appropriate unit for describing the rate of growth of a seedling because seedling will not grow some millimeters in a minute, which is not appropriate.
miles per hour is not the appropriate unit for describing the rate of growth of a seedling because 'miles' unit is used for describing distance traveled.
grams per second is not the appropriate unit for describing the rate of growth of a seedling because 'grams' unit is used describing the weight(or quantity).
millimeters per week is the appropriate unit for describing the rate of growth of a seedling because seedling will grow some millimeters in a week, which is quiet appropriate.
