b) Sears Tower

The Sears Tower, now known as the Willis Tower, was the tallest building constructed in the 20th century in the U.S., symbolizing architectural ambition and innovation. Completed in 1973 in Chicago, Illinois, it stood as the world’s tallest building for nearly 25 years. The tower’s design, featuring a bundled tube structure, was revolutionary in the field of skyscraper engineering. This architectural marvel not only dominated the Chicago skyline but also represented a milestone in high-rise construction, reflecting the era’s technological advancements and the drive to achieve new heights in architectural design.