Final answer:
The correct answer is Santiago Calatrava. The Chicago Spire, designed by Santiago Calatrava, was planned to become the tallest structure in North America, but the project was never completed.
Step-by-step explanation:
The correct answer is C. Santiago Calatrava.
Designed by architect Santiago Calatrava, the Chicago Spire was planned to become the tallest structure in North America. However, the construction of the Chicago Spire was never completed, and the project was eventually canceled due to financial difficulties in 2008.
It is important to note that the current tallest building in North America is the One World Trade Center in New York City, which was completed in 2014.