The table shows the proof of the relationship between the slopes of two parallel lines. What is the missing reason for step 2?
[tex]\[
\begin{tabular}{|l|l|}
\hline
\textbf{Statements} & \textbf{Reasons} \\
\hline
1. $r \parallel s$ & given \\
\hline
2. $m_{ r }=\frac{d-b}{c-0}=\frac{d-b}{c}$ & \textbf{?} \\
\hline
3. $m_{ s }=\frac{0-a}{c-0}=-\frac{a}{c}$ & \\
\hline
4. Distance from $(0, b)$ to $(0, a)$ equals the distance from $(c, d)$ to $(c, 0)$ & Definition of parallel lines \\
\hline
5. $d-0=b-a$ & Application of the distance formula \\
\hline
6. $m_{ r }=\frac{(b-a)-b}{c}$ & Substitution property of equality \\
\hline
7. $m_{ r }=\frac{a}{c}$ & Inverse property of addition \\
\hline
8. $m_{ r }=m_{ s }$ & Substitution property of equality \\
\hline
\end{tabular}
\][/tex]
What is the missing reason for step 2?
A. Pythagorean theorem
B. Application of the slope formula
C. Transitive property
D. Application of the distance formula