Based on this scatterplot visualization from Lab $5\mathrm{.}1$ Excel, Evaluating the Relationship Between Sales and R&D Expenditures, which would you consider to be the independent variable?

The y axis ranges from $0$ to $70000000$ and the x axis ranges from $0$ to $4000000.$ A dotted line representing lineat revenues rises from about $(1000000,17500000)$ to $(4000000,45000000).$ The dots are concentrated between $1000000$ and $3000000$ on the x axis and $20000000$ and $40000000$ on the y axis.

Revenues $($Sales$)$

R&D Expenditures

Cannot determine