Answer: Choice C
Graph with filled in circles at d = 0 and d = 2, shading in between
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Explanation:
d = amount downloaded in gigabytes
The smallest amount is d = 0. We cannot download a negative amount of data, so this is why d = 0 is the smallest.
The largest amount allowed is d = 2. This is the cap that the ISP has set up.
So basically d can be anything between d = 0 and d = 2, including both endpoints. This means
We use filled in circles for both endpoints to show to the reader "include these endpoints". Shading is done in between to show the entire solution set of possible d values. For instance d = 1 is in that region so it is possible to have this solution. Something like d = 4 is outside the region and not possible.