Final answer:
Science stalled after Democritus due to the rise of mysticism, the fall of the Roman Empire, and the ensuing Dark Ages, which saw a decline in literacy and education until the Renaissance era.
Step-by-step explanation:
The reason why science stagnated after Democritus involves a variety of factors, including socio-cultural and political changes. One significant aspect that contributed to this was the rise of mysticism and religious doctrines that displaced empirical inquiry, which aligns with multiple choice option 'D'. Furthermore, during the medieval period, the science of ancient civilizations such as Greek and Roman knowledge was often preserved in monasteries rather than being explored or expanded upon. This period, sometimes referred to as the Dark Ages, saw a decline in literacy and structured education as the former Roman Empire's infrastructure collapsed, making the funding and transmission of scientific knowledge more difficult. This trend continued until the Renaissance, which marked a revival of interest in ancient texts and the emergence of modern scientific inquiry.