D - that his father should embrace life for as long as possible.
The poem "Do Not Go Gentle Into That Good Night" by Dylan Thomas is a plea to his father (and all people) to fight against death and to embrace life for as long as possible. The refrain "Rage, rage, against the dying of the light" emphasizes the poet's call to action for his father to resist death and to continue to live with passion and energy. The other refrain, "Do not go gentle into that good night," also reinforces this idea and emphasizes the urgency of the message. Therefore, option D is the correct answer.