the type of hair their parents have the type of hair their brothers and sisters have their hair color their skin color
I gave my students this multiple choice question: Some people have straight hair and some have curly hair. What decides whether a person will be born with curly hair or straight hair?

Only one answer is correct among these 4 choices:
- the type of hair their parents have
- the type of hair their brothers and sisters have
- their hair color
- their skin color

Could you tell me which one is correct?

the type of hair their parents have