The correct answer d. one of the atoms sharing electrons is much more electronegative.
Explanation:
If one of the atoms is more electronegative than the others, like the oxygen in the water molecule, it will allow this atom to attract the other's electrons turning itself into a negative pole and turning the others into a positive pole. In the water, oxygen is more electronegative and that's why it becomes the negative part and the hydrogens become the positive.
