Answer:
D. He cannot capture his beloved's beauty in verse.
Explanation:
In the Sonnet 18, Francesco Petrarch expresses his feelings about how desperately he wants to write about his beloved. Although his beloved had died, his pen and hand are not extending their support to write about his beloved. He finds it difficult to express her beauty in words. This is the major cause of his disappointment. He is unable to express his beloved's goodness and praise her beauty which makes him sad and remorse.