Final answer:
The global transition to fully modern Homo sapiens was completed by about 25,000 yBP, as modern humans had reached all continents, including Siberia, and the multiregional evolution model suggests that all modern humans evolved from Homo erectus in Asia, but this is less supported than the 'out of Africa' model.
Step-by-step explanation:
The transition to fully modern Homo sapiens was completed globally by about 25,000 yBP. This corresponds to choice d. By this time, modern humans had spread throughout Africa, Asia, Europe, and Australia. Evidence suggests that modern humans had reached Siberia by about 25,000 years ago. Moreover, according to some sources, it seems that they arrived in the Americas between 16,000 to 13,000 years ago, completing the global spread of the species.
The multiregional evolution model is described by statement b, suggesting that all modern humans evolved from a population of Homo erectus in Asia. However, most scientific consensus supports the 'out of Africa' model, which asserts that modern humans originated in Africa about 200,000 years ago and later spread across the globe.