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]: What did the principle of inertia do for general relativity?, Context: The concept of inertia can be further generalized to explain the tendency of objects to continue in many different forms of constant motion, even those that are not strictly constant velocity. The rotational inertia of planet Earth is what fixes the constancy of the length of a day and the length of a year. Albert Einstein extended the principle of inertia further when he explained that reference frames subject to constant acceleration, such as those free-falling toward a gravitating object, were physically equivalent to inertial reference frames. This is why, for example, astronauts experience weightlessness when in free-fall orbit around the Earth, and why Newton's Laws of Motion are more easily discernible in such environments. If an astronaut places an object with mass in mid-air next to himself, it will remain stationary with respect to the astronaut due to its inertia. This is the same thing that would occur if the astronaut and the object were in intergalactic space with no net force of gravity acting on their shared reference frame. This principle of equivalence was one of the foundational underpinnings for the development of the general theory of relativity.
[A]: one of the foundational underpinnings


[Q]: Who has studied the Mahayana?, Context: There is no evidence that Mahāyāna ever referred to a separate formal school or sect of Buddhism, but rather that it existed as a certain set of ideals, and later doctrines, for bodhisattvas. Initially it was known as Bodhisattvayāna (the "Vehicle of the Bodhisattvas"). Paul Williams has also noted that the Mahāyāna never had nor ever attempted to have a separate Vinaya or ordination lineage from the early schools of Buddhism, and therefore each bhikṣu or bhikṣuṇī adhering to the Mahāyāna formally belonged to an early school. This continues today with the Dharmaguptaka ordination lineage in East Asia, and the Mūlasarvāstivāda ordination lineage in Tibetan Buddhism. Therefore Mahāyāna was never a separate rival sect of the early schools. From Chinese monks visiting India, we now know that both Mahāyāna and non-Mahāyāna monks in India often lived in the same monasteries side by side.
[A]:
Paul Williams