Answer
The most appropriate viewing rectangle is (iii).
Also see the image below.
Work Step by Step
By simply graphing the function for all of the given viewing rectangles, we can visually determine which of the viewing rectangle is the most appropriate.
The most appropriate viewing rectangle has to include all of the main/critical points and curves of the graph.
As you can see in the image above, the most appropriate viewing rectangle is third $(iii)$ one. Across the borders of the rectangle provided we have not any significance change in the graph.
$(i)$ In the first viewing rectangle it is too much zoomed in. This way we will lose a lot of main points of the graph. Such as $y$-intercept and $x$-intercept, also the form of curves.
$(ii)$ In this case we will not be able to see how the graph continues on the left-hand side. We cannot see whether it stops there, goes down/up or etc.
$(iii)$ This one is appropriate. We have every main point of the graph provided. On the left-hand side it continues unbounded, so we don't need to see it further.
$(iv)$ This one is too broad. We won't be able to see any of the point of the graph properly.
