Question

The answer choices are:A. Definition of complementary anglesB. Definition of a linear pairC. Simplification of equation from previous step D. Substitution

Answer 1

For the fourth step shown in the "Reasons"

$\angle ANV+\angle ANR=180$

Note that both angles lie on the same straight line which is line RV.

Angles on a straight line sum up to 180 degrees.

Therefore,

$\begin{gathered} \angle ANV+\angle ANR=180\text{ } \\ \text{Both angles are a linear pair} \end{gathered}$

The answer is option B; Definition of a linear pair