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

[Q]: 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.
[A]: black box

[Q]: Which of the following did not occur in the 20th century: urbanization, the spread of the Ottoman Empire, or wars?, Context: South Slavic historically formed a dialect continuum, i.e. each dialect has some similarities with the neighboring one, and differences grow with distance. However, migrations from the 16th to 18th centuries resulting from the spread of Ottoman Empire on the Balkans have caused large-scale population displacement that broke the dialect continuum into many geographical pockets. Migrations in the 20th century, primarily caused by urbanization and wars, also contributed to the reduction of dialectal differences.
[A]: spread of Ottoman Empire

[Q]: What did the pop up stores sell most?, Context: Microsoft began an advertising campaign centered around Windows 8 and its Surface tablet in October 2012, starting with its first television advertisement premiering on October 14, 2012. Microsoft's advertising budget of US$1.51.8 billion was significantly larger than the US$200 million campaign used to promote Windows 95. As part of its campaign, Microsoft set up 34 pop-up stores inside malls (primarily focusing on Surface), provided training for retail employees in partnership with Intel, and collaborated with the electronics store chain Best Buy to design expanded spaces to showcase devices. In an effort to make retail displays of Windows 8 devices more "personal", Microsoft also developed a character known in English-speaking markets as "Allison Brown", whose fictional profile (including personal photos, contacts, and emails) is also featured on demonstration units of Windows 8 devices.
[A]:
Surface