The fraternal birth order effect refers to a factor associated with:

The right answer is sexual orientation. several studies have shown that the order of birth of the siblings (only those of the male sex) increases the probability of developing a homosexual sexual orientation in at least 28-48% of cases. that is if a person is born 5th in a family where their 4 older siblings are men, their chances of developing a homosexual sexual orientation is greater. the investigations hypothesize that this could be due to an autoimmune process that occurred in the womb during the gestation process. i hope this information can you.

Idont know which one is right   but i know that c is wrong and a might be wrong