Let points R, S, T be the midpoints of segments AC, AB, and CB.
Triangle midline theorem states that the line segment connecting the midpoints of two sides of a triangle is parallel to and half the length of the third side.
Thus, the midline RS (where R is a midpoint of AC and S is the midpoint of AB) is parallel to BC and is half the length of the side BC:
[tex]RS=\dfrac{1}{2}BC.[/tex]
Answer: correct choice is A
