Which graph corresponds to an object moving with a constant negative acceleration and a positive velocity?

Let acceleration be $a$.
Given that $a=-C$
We know that, $a=$$\frac{vdv}{dx}=-C$
$vdv=-Cdx$

Integrating the above equation,
$\frac{v^2}{2}=-Cx+k$.

Thus, the velocity-distance graph is

The distance cover by the object is $x= -\frac{v^2}{2C}+\frac{k}{C}$.

Thus, with the increase in distance, velocity decreases.

Now, $a=-C=\frac{dv}{dt}$

$$\begin{gathered} \Rightarrow dv=-Cdt \\ \Rightarrow v=-Ct+u , \left(\text{straight line}\right) \end{gathered}$$