Question

(a) one pair of angles that form a linear pair (b) one pair of vertical angles (c) one pair of angles that are congruent (a) linear pair: ∠ and ∠ (b) vertical angles: ∠ and ∠ (c) congruent angles: ∠ and ∠

Explanation:

Step1: Identify linear - pair

A linear pair of angles are adjacent and supplementary. $\angle1$ and $\angle2$ share a common side and their non - common sides form a straight line.

Step2: Identify vertical angles

Vertical angles are formed when two lines intersect. $\angle1$ and $\angle4$ are vertical angles as they are opposite each other at the intersection of lines $l$ and $n$.

Step3: Identify congruent angles

Vertical angles are congruent. So $\angle1$ and $\angle4$ are congruent. Also, if the lines $l$ and $m$ are parallel, corresponding angles are congruent. For example, $\angle1$ and $\angle5$ are congruent if $l\parallel m$. Here we can choose vertical angles as an example of congruent angles.

Answer:

(a) $\angle1$ and $\angle2$
(b) $\angle1$ and $\angle4$
(c) $\angle1$ and $\angle4$