The mistake is in Step #4. The correct statement should indicate that the line should be drawn through point C, but it should not include points A and B. Thus, the correct option is:
Step #4 has a mistake. It should say: “Use a straight edge to draw a line that passes through point C (but not points A and B). This line is a bisector of AB¯¯¯¯¯¯¯¯.”
This correction is necessary because the line segment bisector is defined as the line that passes through the midpoint (point C) and is perpendicular to line segment AB, not a line that goes through points A and B.