State which sampling method is being described.

A) To determine the average number of hours people spend per day watching television, a researcher divides the population into groups according to age. Then he randomly selects 50 people from each age group.

B) To study the migratory behavior of loons, biologists randomly tag 64 loons in the Great Lakes.

C) As melons are unloaded from a truck, Elio picks every 10th melon until he collects 80 melons to estimate the average mass of the melons.