#### Answer

slope=undefined

#### Work Step by Step

Slope is defined as:
$\displaystyle slope=\frac{rise}{run}$
To find the slope of $CD$, we need to find the rise and run from $C$ to $D$. From the graph, we see that:
$rise=-7$ units
$run=0$ units (since the line is vertical)
Thus:
$slope=\frac{-7}{0}=undefined$ (vertical "infinite" slope)