The mistake in Liam's plan is in Step #4. The correct adjustment should indicate that the line drawn is only through point C, which is the midpoint, not through points A and B. Therefore, the correct response 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 emphasizes that line segment AC and CB are equal, making line segment CB the bisector of AB¯¯¯¯¯¯¯¯.