Answer: The shore's a backdrop for my lonely day.
Step-by-step explanation:
This quatrain's rhyme scheme is such that a line must rhyme with the line that follows after the next line. This is why lines 1 and 3 rhyme by ending with the words: "alone" and "flown".
We need to pick an option therefore, that has a last word that can rhyme with the word "stay" in line 2. That option is the one above which has "day" at it's end. "Day" and "stay" rhyme so this is the correct answer.