Answer:
12) Line segment AB

13) Line segment CD

14) Line segment EF

15) Line segment GH

16) Line segment IJ

17) Line segment KL

18) Line segment MN

19) Line segment OP

20) Line segment QR

21) Line segment ST

Step-by-step explanation:
Coordinates are now described:
,
,
,
,
,
,
,
,
,
,
,
,
,
,
,
,
,
,
, 
The slope of each line segment is calculated by applying definition of secant line:
12) Line segment AB

13) Line segment CD

14) Line segment EF

15) Line segment GH

16) Line segment IJ

17) Line segment KL

18) Line segment MN

19) Line segment OP

20) Line segment QR

21) Line segment ST
