Dumb question? or testing external knowledge?

Results are out for the science section of our "National Report Card" (NAEP exams). The news is that the US had pathetic results, surprise!

I was looking through the sample questions and came to this question (click for full-size image:)


The correct answer is, of course, D; however, I don't see how you can possibly answer that question based on the "web" they showed. According to the graphic, decomposers are the ultimate consumers, in the end, eating everything. But the graphic does not show them being the food source of anything.

Despite the top part of the question stating "use the information in the food web to answer the questions that follow," the only way you could answer that question is to ignore the graph and use your own knowledge of the topic.