Final answer:
DC transmission started before the options given, closely related to milestones in communications technology at the end of the 19th century and the start of the 20th century.
Step-by-step explanation:
The initiation of Direct Current (DC) transmission occurred far earlier than any of the options presented in the question. However, if we consider the communications technology milestones and the advancements made towards the end of the 19th century and the start of the 20th century, one could argue that the closest answer to the developmental phase of DC transmission - in the context of electrical and not digital transmission - would be towards the end of the 1800s. This period saw significant advances in telecommunications, such as the completion of the first transatlantic telegraph line in 1858 and the patenting of the telephone by Alexander Graham Bell in 1876. The advent of wireless signal transmission by Guglielmo Marconi in 1901 further demonstrates the rapid development of communications technology during this era.