Answer: d. All of the above are true.
Step-by-step explanation:
The apple is thought to symbolize the apple eaten by Adam in the Bible, largely based on the title, The Son of Man. Also it is also true that many who view this piece feel uncomfortable about the image, because many can relate to this image and the sense of having temptation in front of others. Additionally, it is also true that one theory about this painting is that it represents the temptations always directly facing mankind, no matter what the time or space.
Therefore option (d) is the correct answer, which means all are true.