Final answer:
The lines quoted are from the poem 'Walking Away' by C. Day Lewis and are not found in any of the options provided.
Step-by-step explanation:
The lines "Selfhood begins with a walking away, And love is proved in the letting go" come from a poem by C. Day Lewis titled 'Walking Away', which is frequently studied in English literature courses. This poem is not found in any of the listed literary works from the options provided, such as 'To Kill a Mockingbird' by Harper Lee, 'The Great Gatsby' by F. Scott Fitzgerald, 'The Road Not Taken' by Robert Frost, or 'A Portrait of the Artist as a Young Man' by James Joyce. As a result, all these options are incorrect. It is important to note when studying literature to verify the source of specific lines to ensure proper credit to authors and an accurate understanding of literary works.