Answer:
2. RS = ST, Reason: Midpoint of a line (definition)
4. RS = XY, Reason: Transitive Property of congruence (if a=b, and b=c, a=c)
Explanation:
A Midpoint divides a line exactly in half, due to the definition of a Midpoint. So, RS = ST, since they measure the same distance from the Midpoint. RS=XY because of the Transitive Property of Congruence. If ST = XY, and RS = ST, then RS = XY.