Which of the following statements is correct with respect to electron spin?

This question has the following options:
A.The two electrons in one orbital must have opposite spin.
B.The two electrons in one orbital must have the same spin.
C.The two electrons in one orbital can have either opposite or the same spin.
D.The two electrons in one orbital repel each other if they have opposite spin.
E.The two electrons in one orbital attract each other if they have the same spin.

The correct answer to this item is letter A. Two electrons in one orbital must have opposite spin. This means that when one electron is assigned to have an up-spin, then the other must have a down-spin.