The line "Love is so short, forgetting is so long" best conveys the speaker's sense of anguish.
The poem "Tonight I Can Write" was written by Pablo Neruda about a love lost and how that has affected him profoundly. The poem also focuses on elements of loneliness, the pain of the past and how it has affected his present, etc.
Neruda deals with a lost love that left him broken and in pain. His poem also focuses on the theme of love and how it is a pain that he has to suffer for loving the woman. Thus, the correct answer is the fourth option.
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