Teacher: The task is about reading the given story and question, then finding an answer to the given question. Based on the passage provided and the given question, you should identify the shortest continuous text span from the passage that serves as an answer to the given question. Avoid answers that are incorrect or provides incomplete justification for the question.
Teacher: Now, understand the problem? If you are still confused, see the following example:
story : Honolulu is the capital and largest city of the U.S. state of Hawaii. It is an unincorporated part of and the county seat of the City and County of Honolulu on the island of Oahu. The city is the main gateway to Hawaii and a major portal into the United States. The city is also a major hub for international business, military defense, as well as famously being host to a diverse variety of east-west and Pacific culture, cuisine, and traditions. 

Honolulu is the most remote city of its size in the world and is the westernmost major U.S. city. For statistical purposes, the U.S. Census Bureau recognizes the approximate area commonly referred to as "City of Honolulu" (not to be confused with the "City and County") as a census county division (CCD). Honolulu is a major financial center of the islands and of the Pacific Ocean. The population of the city of Honolulu was 337,256 as of the 2010 census, while the Honolulu CCD was 390,738 and the population of the consolidated city and county was 953,207. 

"Honolulu" means "sheltered harbor" or "calm port". The old name is said to be Kou, a district roughly encompassing the area from Nuuanu Avenue to Alakea Street and from Hotel Street to Queen Street which is the heart of the present downtown district. The city has been the capital of the Hawaiian Islands since 1845 and gained historical recognition following the attack on Pearl Harbor by Japan near the city on December 7, 1941. question: What does Honolulu mean?
Solution: sheltered harbor
Reason: This answer for the given question is based on the following sentence from the passage - "Honolulu" means "sheltered harbor" or "calm port" and this is answerable from the passage. So, it is a good answer.

Now, solve this instance: story: Omaha is the largest city in the state of Nebraska and the county seat of Douglas County. Omaha is located in the Midwestern United States on the Missouri River, about north of the mouth of the Platte River. Omaha is the anchor of the Omaha-Council Bluffs metropolitan area, which includes Council Bluffs, Iowa, across the Missouri River from Omaha. According to the 2010 census, Omaha's population was 408,958, making it the nation's 44th-largest city; this had increased to 446,970 as of a 2016 estimate. Including its suburbs, Omaha formed the 60th-largest metropolitan area in the United States in 2013, with an estimated population of 895,151 residing in eight counties. The Omaha-Council Bluffs-Fremont, Nebraska-IA Combined Statistical Area is 931,667, according to the U.S. Census Bureau's 2013 estimate. Nearly 1.3 million people reside within the Greater Omaha area, comprising a 50-mile (80 km) radius of Downtown Omaha, the city's center. 

Omaha's pioneer period began in 1854, when the city was founded by speculators from neighboring Council Bluffs, Iowa. The city was founded along the Missouri River, and a crossing called Lone Tree Ferry earned the city its nickname, the "Gateway to the West". Omaha introduced this new West to the world in 1898, when it played host to the World's Fair, dubbed the Trans-Mississippi Exposition. During the 19th century, Omaha's central location in the United States spurred the city to become an important national transportation hub. Throughout the rest of the 19th century, the transportation and jobbing sectors were important in the city, along with its railroads and breweries. In the 20th century, the Omaha Stockyards, once the world's largest, and its meatpacking plants gained international prominence., question: What was the event called?
Student:
the Trans-Mississippi Exposition