Explanation:

Introduction:
The last name of a person is also known as their surname. It is a part of a person's full name and is typically inherited from their family. The last name is an important identifier and is used to distinguish individuals from one another.

Detailed Explanation:
- Common name: The common name of a person refers to the name by which they are commonly known or called. It can be their first name, nickname, or any other name they are commonly addressed by. The last name is not the same as the common name.
- Real name: The real name of a person refers to their legal or given name. It includes both their first name and last name. The last name is a part of the real name but does not refer to the entire real name.
- Surname: The last name of a person is also known as their surname. It is the family name passed down from generation to generation. The surname is usually shared by family members and helps to identify a person's lineage or ancestry.
- All of these: Option 'C' states that the last name is all of the above mentioned - a common name, real name, and surname. This is because the last name is a part of the person's real name, which is their legal name, and it is also their surname, which is their family name.

Conclusion:
In conclusion, the last name of a person is their surname. It is a part of their real name and is inherited from their family. The last name is an important identifier and helps to distinguish individuals from one another.