SAT Question 70ebd3d0: Nonlinear Functions answer and explanation with Desmos solution

Choice D is correct. The function $N$ is exponential, so it follows that $N(d)$ changes by a fixed percentage for each increase in $d$ by $1$. Since $d$ is measured in hundreds of meters, it also follows that the number of brachiopod species changes by a fixed percentage for each increase in ocean depth by $100$ meters. Since the base of the exponent in the model is $0.90$, which is less than $1$, the number of brachiopod species decreases as the ocean depth increases. Specifically, the number of brachiopod species at a depth of $d+100$ meters is $90\%$ of the number of brachiopod species at a depth of $d$ meters. This means that for each increase in ocean depth by $100$ meters, the number of brachiopod species decreases by $10\%$.