Read the excerpt from "Save the Coral Reefs." Coral receives most of its oxygen and food from the algae that live in and on the reefs. When the coral becomes stressed by the overheating of the ocean caused by global warming, the algae detach from the reefs, and the reefs lose their main source of sustenance. The reefs are then bleached into a whitish color, and have trouble growing and reproducing.

Using context clues as a guide, what is the meaning of "sustenance" in this passage?

A) the living space of the coral reef
B) growth for the coral reef
C) the color of the coral reef
D) nourishment for the coral reef​