Answer: You could argue both points, but here is my interpretation of choice “a”:
a. It highlights the human tendency to look back at our choices and regret the decisions we have made.
Explanation: The speaker tried to evaluate both paths, looking as far as one could, to determine which was less traveled. They make their choice but then question if it was truly less traveled, as both “had worn them really about the same.” The speaker says they’ll come back to the other path another day, but then immediately doubts they’ll return. Sighing, the speaker recounts this choice at a later time and then claims to have ultimately taken the one less traveled, which made “all the difference” in his/her life.