Final answer:
After the Great Fire of London in 1666, Christopher Wren proposed a radial design for the city's reconstruction, which remained largely unrealized, with London being rebuilt on its original medieval street plan. The correct urban form that Wren designed for London is identified as the Radial City.
Step-by-step explanation:
After the Great Fire of London in 1666, Christopher Wren was instrumental in the city's rebuilding efforts. While he is renowned for his work on the magnificent St. Paul's Cathedral, extant records of his plans for London suggest a radial design, which focused on rebuilding with grand boulevards radiating from key landmarks, such as the newly designed St. Paul's Cathedral. However, it is essential to clarify that although Wren proposed a radical redesign for London, his plans for a radial city were never fully realized due to a variety of reasons, including property rights and the urgent need for the city to rebuild quickly. Instead, London was rebuilt using the existing medieval street plan. Therefore, the correct answer is d. What is the Radial City?