On December 12, 1901, a radio transmission received by Guglielmo Marconi resulted in the first transmission of a transatlantic wireless signal (Morse Code) from Poldhu, Cornwall, to St. John's, Newfoundland.

The correct answer is option 'D', the 1900s. The first transatlantic radio broadcast occurred in the early 20th century, specifically in the year 1901. This remarkable event marked a significant milestone in the history of communication and technology.

The Transatlantic Radio Broadcast in 1901:

1. Guglielmo Marconi and the Wireless Telegraph:
- Guglielmo Marconi, an Italian inventor and physicist, is credited with the development of wireless telegraphy.
- In the late 19th century, Marconi conducted extensive experiments and research on wireless communication using electromagnetic waves.

2. The Experiment at Signal Hill, Newfoundland:
- In December 1901, Marconi performed a groundbreaking experiment at Signal Hill in St. John's, Newfoundland (Canada).
- He successfully transmitted the letter "S" in Morse code from a transmitting station to a receiver located approximately 2,200 miles away in Poldhu, Cornwall (United Kingdom).

3. The Importance of the Transatlantic Radio Broadcast:
- The transatlantic radio broadcast was a significant achievement because it demonstrated the feasibility of long-distance wireless communication.
- It paved the way for further advancements in global communication, ultimately leading to the development of modern radio, television, and other forms of wireless transmission.

4. Impact and Legacy:
- Marconi's successful experiment sparked widespread interest and enthusiasm for wireless telegraphy.
- It led to the establishment of communication networks, the construction of radio stations, and the continued development of technology in the field of telecommunications.

Conclusion:
The first transatlantic radio broadcast occurred in the 1900s, specifically in 1901. This event, led by Guglielmo Marconi, marked a significant breakthrough in wireless communication technology. The successful transmission of the letter "S" in Morse code over a distance of 2,200 miles demonstrated the potential for long-distance communication and paved the way for the development of modern radio and other wireless technologies.