In this task, you are given a question and a context passage. You have to answer the question based on the given passage.

What does every plane have?, Context: Grey-box testing (American spelling: gray-box testing) involves having knowledge of internal data structures and algorithms for purposes of designing tests, while executing those tests at the user, or black-box level. The tester is not required to have full access to the software's source code.[not in citation given] Manipulating input data and formatting output do not qualify as grey-box, because the input and output are clearly outside of the "black box" that we are calling the system under test. This distinction is particularly important when conducting integration testing between two modules of code written by two different developers, where only the interfaces are exposed for test.
black box

Seattle is one of the what of the country?, Context: Of the city's population over the age of 25, 53.8% (vs. a national average of 27.4%) hold a bachelor's degree or higher, and 91.9% (vs. 84.5% nationally) have a high school diploma or equivalent. A 2008 United States Census Bureau survey showed that Seattle had the highest percentage of college and university graduates of any major U.S. city. The city was listed as the most literate of the country's 69 largest cities in 2005 and 2006, the second most literate in 2007 and the most literate in 2008 in studies conducted by Central Connecticut State University.
69 largest cities

Which city was mentioned fourth?, Context: In the wake of the United States' economic downturn and the legalization of gambling in adjacent and nearby states (including Delaware, Maryland, New York, and Pennsylvania), four casino closures took place in 2014: the Atlantic Club on January 13; the Showboat on August 31; the Revel, which was Atlantic City's second-newest casino, on September 2; and Trump Plaza, which originally opened in 1984, and was the poorest performing casino in the city, on September 16.
Pennsylvania