Final answer:
Abby can use a two-column proof to show that Q is equidistant from S and T when CD is a perpendicular bisector of ST.
Step-by-step explanation:
In order to prove that if segment CD is a perpendicular bisector of segment ST, then any point, Q, on segment CD is equidistant from endpoints S and T, Abby can use a two-column proof. In the left column, Abby can list the given information and any relevant definitions or theorems.
In the right column, Abby can apply the definitions and theorems to make logical statements and justifications, ultimately leading to the conclusion that Q is equidistant from S and T. Each step should be clearly stated and supported with reasoning.