B. Someone opened the window because he or she was too warm.
The use of "he or she" is correct here because at the beginning of the sentence uses the word "someone" which is singular and the two must correspond, so the that one must be singular as well so it can't be "they" or "them"
Just listen to your mom because you need to make your bed and be respectful
I think you meant external conflict?
It would be person V.S. person or Person V.S environment