Context: Below is a food web from Shenandoah National Park, a forest ecosystem in Virginia.
A food web models how the matter eaten by organisms moves through an ecosystem. The arrows in a food web represent how matter moves between organisms in an ecosystem.
Which of the following organisms is the decomposer in this food web?
A. gray fox
B. black bear
C. swallowtail caterpillar
D. bolete fungus
Pick the correct answer from the listed options and provide the letter of the selected option.

D