A parallel sentence mentions the same grammatical expression twice. I would go with "D". 'Passed' and 'Demonstrated' are both past tense words that express the same past tense grammatical idea.
If you have more questions, feel free to ask me.
Answer would be conflict. Antagonist is essentially the protagonist's enemy.
It means the scientific study of sight and the behavior of light, or the properties of transmission and deflection of other forms of radiation
