Answer:
Option: C is the correct answer.
C) Use the straightedge to draw the line through points C and D.
Step-by-step explanation:
Katie is constructing the circumscribed circle for △RST.
The next step in the construction of the circumscribed circle is:
Use the straightedge to draw the line through points C and D.
( Since on drawing a straight edge that passes through point C and D we get a point where the line AB and CD meets that point will be considered as the center of the circumscribed circle ).
Hence, option: C is correct.