It shows the doer of the action.It comes before verb and indicates this action or work is done by it/him/her etc.Ex.Susan switched off the lights. Who switched off the lights? The answer is Susan (subject of the sentence)
C is the answer. Because deleterious is the opposite of helpful. And ominous is the opposite of friendly.
They are alike bc the earth rotate to am pm and night and it starts a new day.