How is the mean annual rainfall of a given place calculated using records for 35 years?

• A by summing the yearly average rainfall figure and dividing by 35
• B by summing the yearly total rainfall figures dividing by 35
• C by summing the yearly total rainfall figures for 35 years and dividing by 12
• D by finding the average between the figures for the wettest and the the direst years and multiplying by 35
• E by plotting the rainfall figures on a graph and finding the midpoint