The first multicellular organism to have its genome fully sequenced, C. elegans is a nematode that lives in soil, feeds on bacteria, and reaches about 0.04 in (1 mm) in length. Its small genome and transparent skin have led it to be widely used as a “model organism” by geneticists and developmental biologists. Because it experiences the same symptoms as humans undergo when they stop using a certain product, C. elegans has been identified as a model for dependence on what substance? Discuss
Source: The Free Dictionary