Answer: d.The speaker describes how he fears that his blindness may prevent him from serving God through poetic writing.
Sonnet XIX is an extremely personal reflection on life and purpose by Milton, who was struggling with the idea of going blind. The first section of the poem discusses his main worry, and that is the fact that he will no longer be able to continue God's work by using his talent for poetry. However, throughout the poem, he reflects on this notion and on the opportunities that life can still afford him, and he concludes in a more hopeful note.