What characteristics of hair differ in the human population?

The characteristics of hair that differ in the human population are the following:1. Human hair color- it is the hair follicles pigmentation which is because of the two types of melanin: pheomelanin and eumelanin. If there are more eumelanin present in the hair, its color will be darker, and vice versa. The darker the hair of a person is, there will be more individual hair follicles on their scalp.2. Hair Quantity- There are humans who are suffering from hair loss which refers to losing hair from a part of the head or body. There are also others who have hirsutism which refers to having excessive body hair in both men or women. 

The answer is c establishing proper sleep hygiene