Answer
slope=0
Work Step by Step
Slope is defined as:
$\displaystyle slope=\frac{rise}{run}$
To find the slope of $BC$, we need to find the rise and run from $B$ to $C$. From the graph, we see that:
$rise=0$ units (since the line is horizontal)
$run=-4$ units
Thus:
$slope=\frac{0}{-4}=0$