The answer is C: It compares the stars' reflections to diamonds to suggest the idea of beauty in nature.
The metaphor used here, in poetic terms, is stating that, as the stars reflect on the surface of the ocean, one can marvel at the beauty of such an occurrence in nature, and since the image shows not the influence of man on the occurrence, it is then perfectly comprehensible to interpret the metaphor as one referring to the beauty in nature.
