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

What is the name of the discipline of the person Gregory of Tours reads?, Context: Even as the Western Roman empire collapsed, literate men acknowledged that Virgil was a master poet. Gregory of Tours read Virgil, whom he quotes in several places, along with some other Latin poets, though he cautions that "we ought not to relate their lying fables, lest we fall under sentence of eternal death."
poet

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

What moved on keels?, Context: In the Sandgate area, to the east of the city and beside the river, resided the close-knit community of keelmen and their families. They were so called because they worked on the keels, boats that were used to transfer coal from the river banks to the waiting colliers, for export to London and elsewhere. In the 1630s about 7,000 out of 20,000 inhabitants of Newcastle died of plague, more than one-third of the population. Specifically within the year 1636, it is roughly estimated with evidence held by the Society of Antiquaries that 47% of the then population of Newcastle died from the epidemic; this may also have been the most devastating loss in any British City in this period.
coal