Which plot development would most logically lead a reader to conclude that the themes of this story are developing loyalty and creating sense of family?

the answer is going to be a

The answer should be A) The twin experiences an ilness and the flight attendant helps her through it.

Explanation:

When someone that is close to you feels sick, you feel the necessity to comfort him/her in orde ot get better, this is because the link you have with this persons makes you ensure its survival. In this case, since she's feeling ill and they have a connection for their relationship (without knowing it) she feels something quite similar to this reaction. There are some other theories tht assure that twins get to feel the same sensations their twin has without even seeing them.

Let me know if you have any question :D