Which One of the Following Examples Most Clearly Illustrates How

Which one of the following examples most clearly illustrates how mental set can interfere with problem solving?

A) Annabeth wants to make amends with a boyfriend she recently fought with.However, the boy tells her that he is now dating someone else.
B) Bernadette needs to calculate the volume of a pyramid.She knows she learned the correct formula in class, but she cannot seem to remember it now.
C) Kali is working on a jigsaw puzzle.One of the pieces to the puzzle is missing.
D) Margaret-Ann's car will not start.It does not occur to her that she can take the bus to work because she has always driven her car to work.