Which of the following is a major industry in Illinois?

Agriculture is considered a major industry in Illinois due to the state's extensive farmland and favorable climate, which contribute to its status as one of the top agricultural producers in the United States. Illinois is particularly well-known for its production of corn and soybeans, which are significant crops both domestically and internationally. The vast agricultural sector also supports various related industries such as food processing, transportation, and agricultural technology.

In contrast, while construction, tourism, and fashion are important sectors, they do not have the same scale or foundational role in Illinois’ economy as agriculture does. Agriculture has deep historical roots in the state's development and contributes significantly to this day, making it a cornerstone of Illinois' economy.