Chapter 1 - Section 1.3 - Early Definitions and Postulates - Exercises - Page 27: 13

(a) $Line~ m$ and $Line~ t$ are parallel. (b) $Line~ m$ and $Line~ p$ are nonparallel.

(a) $Line~ m$ and $Line~ t$ point in the same direction, so they are parallel. (b) $Line~ m$ and $Line~ p$ point in different directions, so they are nonparallel.