The correct answer is A. Arithmetic mean.
The arithmetic mean is the sum of a list of numbers divided by the number of numbers in the list. It is the most common type of average and is often used to represent the central tendency of a data set.
The median is the middle value in a sorted list of numbers. It is often used to represent the central tendency of a data set when the data is skewed.
The geometric mean is the product of a list of numbers, taken to the power of one over the number of numbers. It is often used to represent the central tendency of a data set when the data is multiplicative.
The harmonic mean is the reciprocal of the arithmetic mean of the reciprocals of a list of numbers. It is often used to represent the central tendency of a data set when the data is additive.
In the case of the average rate of growth in population, the arithmetic mean is the most appropriate average to use because it is the most common type of average and is often used to represent the central tendency of a data set. The median and geometric mean are not appropriate because they are not sensitive to changes in the order of the data. The harmonic mean is not appropriate because it is not sensitive to changes in the size of the data.