Detailed Instructions: In this task, you're given an article and an answer. Your task is to generate the fill-in-the-blank question for this answer based on the given article. The blanks are always at the end of the question, and can be filled with more than one word or phrase.
Q: Article: Frank Lloyd Wright probably is the greatest architect that the United States has ever produced. He was very gifted and had a natural ability to design buildings. His buildings were not only beautiful, but they were also practical and useful. They fit their purposes very well. Wright's churches, for example, make people feel like thinking and praying. His office buildings make people enjoy working, and his houses make people feel comfortable at home. However, Frank Lloyd Wright's beautiful, practical and useful buildings are not the only reason that he is famous. There is another reason. Frank Lloyd Wright is called the greatest American architect because he started an American style in architecture. Most of the architecture in the United States before Wright was really European, not American. Wright's buildings do not look like old European buildings. They have their own style. Wright's ideas about style are still used in the United States and in other parts of the world. The most important idea in Frank Lloyd Wright's Style of Architecture is that a building must fit its purpose and the land around it. His houses are often called "grass-land houses" because their lines are similar to the lines on the grassland. Both the lines of the grassland and the lines of Wright's house are parallel to the horizon, the place where earth and sky seem to meet. They are horizontal lines. Most European style houses, in contrast, have many vertical lines that form 90degangles with the horizon.
Answer: not only limited to the U.S
A:
Frank Lloyd Wright's style in architecture was _ .