Chapter 6 - Differential Equations - 6.1 Exercises - Page 404: 59

matches $(d)$

Given $$\frac{dy}{dx}= e^{-2x} $$ So, we get at $x \rightarrow \infty \Rightarrow \frac{dy}{dx}\rightarrow e^{ -\infty}=0 $. This implies that the slope $\rightarrow 0$ at $x \rightarrow \infty $ and that is shown in $(d)$.