Final answer:
Iris's physical traits lead to classifying her based on ethnicity, as these are often inherited and reflect shared ancestral lines, not race, culture, or religion.
Step-by-step explanation:
Iris's physical traits, such as curly red hair, fair white skin, and emerald-green eyes, suggest a biological inheritance from her ancestors. When considering the options provided, such as race, culture, ethnicity, and religion, the most appropriate classification based on physical traits would be ethnicity. Ethnicity refers to groups of people who identify with each other based on shared attributes that typically include ancestral, language, cultural, and sometimes religious backgrounds. The concept of race, in contrast, is a social construct primarily associated with physical characteristics and has been used to categorize people into groups based largely on skin tone, hair type, and eye shape. Culture is about the behaviors, beliefs, and practices of a social group, and religion denotes a system of faith and worship. Therefore, the correct answer to the classification of Iris based on her physical traits that are similar to her grandmother's would be C. ethnicity.