SAT Question 974d33dc: Equivalent Expressions answer and explanation with Desmos solution

Choice A is incorrect and may result from adding the two sets of unlike terms, $r^3$ and $r^2$ as well as $5r^2$ and $8r$, and then adding the respective exponents.

Choice B is incorrect and may result from adding the unlike terms $r^3$ and $r^2$ as if they were $r^3$ and $r^3$ and adding the unlike terms $5r^2$ and $8r$ as if they were $5r^2$ and $8r^2$.

Choice C is incorrect and may result from errors when combining like terms.