Given the model below

Return of Stock $=$ f $($Dividend$,$ Sales, Paid$-$up Capital$)$

Div $=$ Dividend declared by the listed firms

Sales $=$ Net Turnover $($Annual$)$

Capital $=$ Paid$-$up Capital

Form TWO equations to conduct the Chow Test if one intends to study the effect of the Russia$-$Ukraine war using daily trading data from $2021$ Jan $1$ to $2025$ Apr $30.$

$2.$ Based on the model above, using a dummy variable for the Russia$-$Ukraine war, please state the model again.

$3.$ Draw two diagrams for $(1)$ and $(2).$ Explain the difference.

$4.$ What are the benefits of using a dummy variable compared to the Chow Test?