Final answer:
Donald Johanson (option A) is the scientist who discovered the Lucy fossil, an Australopithecus afarensis, in 1974 while on an expedition in Ethiopia.
Step-by-step explanation:
The scientist who discovered the Australopithecus afarensis (Lucy) fossil was Donald Johanson. In 1974, Johanson and his team were on an expedition in Ethiopia when they found approximately 40 percent of a skeleton that turned out to be one of the most famous fossils in the world, Lucy. The fossil was dated to around 3.75-2.8 million years ago (MYA) and it represents a significant discovery in the field of paleoanthropology because it provided substantial insight into the evolution of bipedalism and the physical characteristics of early hominids. Lucy is housed in the Kenya National Museum and carries the designation KNM-AL-288, where KNM stands for Kenya National Museum and AL for the Afar locality where the fossil was found. The discovery of Lucy is a cornerstone in understanding human evolutionary history.