Next time you see an elderly man, check out his nose and ears! While most parts of the human body stop growing as we reach adulthood, studies show that noses and ears continue to grow larger throughout our lifetime. In one study1 examining noses, researchers report "Age significantly influenced all analyzed measurements:" including volume, surface area, height, and width of noses. The gender of the 859 participants in the study was also recorded, and the study reports that "male increments in nasal dimensions were larger than female ones."

(a) How many variables are mentioned in this description?