Final answer:
The Laetoli footprints show that the foot of Australopithecus afarensis was humanlike in having a rounded heel, a nondivergent big toe, and a double arch, meaning the correct answer is (d. all of the above).
Step-by-step explanation:
The Laetoli footprints indicate that the foot of Australopithecus afarensis was humanlike. These footprints suggest this species walked on two legs, similar to modern humans. They demonstrate characteristics such as a nondivergent big toe, which aligns with the rest of the foot rather than sticking out to the side like in other primates. Additionally, the footprints suggest the presence of a double arch, supporting a humanlike bipedal locomotion. While the footprints do indicate a rounded heel, the combination of a nondivergent big toe and a double arch are important markers of bipedalism — similar to humans. Thus, the correct answer is (d. all of the above), indicating that the Laetoli footprints show a rounded heel, a nondivergent big toe, and a double arch, all of which are features that point to a humanlike foot structure.