Q: What is a question about this article? If the question is unanswerable, say "unanswerable".
Infrared tracking, also known as infrared homing, refers to a passive missile guidance system, which uses the emission from a target of electromagnetic radiation in the infrared part of the spectrum to track it. Missiles that use infrared seeking are often referred to as "heat-seekers", since infrared (IR) is just below the visible spectrum of light in frequency and is radiated strongly by hot bodies. Many objects such as people, vehicle engines, and aircraft generate and retain heat, and as such, are especially visible in the infrared wavelengths of light compared to objects in the background.
What is another term for heat seekers?
A: unanswerable

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Judging relationships based on shared characters requires care, since plants may resemble one another through convergent evolution in which characters have arisen independently. Some euphorbias have leafless, rounded bodies adapted to water conservation similar to those of globular cacti, but characters such as the structure of their flowers make it clear that the two groups are not closely related. The cladistic method takes a systematic approach to characters, distinguishing between those that carry no information about shared evolutionary history such as those evolved separately in different groups (homoplasies) or those left over from ancestors (plesiomorphies) and derived characters, which have been passed down from innovations in a shared ancestor (apomorphies). Only derived characters, such as the spine-producing areoles of cacti, provide evidence for descent from a common ancestor. The results of cladistic analyses are expressed as cladograms: tree-like diagrams showing the pattern of evolutionary branching and descent.
How are common ancestries represented for plant families?
A: tree-like diagrams

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During the Middle Ages Aristotle's theory of tabula rasa was developed by Islamic philosophers starting with Al Farabi, developing into an elaborate theory by Avicenna and demonstrated as a thought experiment by Ibn Tufail. For Avicenna (Ibn Sina), for example, the tabula rasa is a pure potentiality that is actualized through education, and knowledge is attained through "empirical familiarity with objects in this world from which one abstracts universal concepts" developed through a "syllogistic method of reasoning in which observations lead to propositional statements which when compounded lead to further abstract concepts". The intellect itself develops from a material intellect (al-'aql al-hayulani), which is a potentiality "that can acquire knowledge to the active intellect (al-'aql al-fa'il), the state of the human intellect in conjunction with the perfect source of knowledge". So the immaterial "active intellect", separate from any individual person, is still essential for understanding to occur.
What does tabula rasa mean?
A: unanswerable

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The formalist definition is that the history of "literature" foregrounds poetic effects; it is the "literariness" or "poeticity" of literature that distinguishes it from ordinary speech or other kinds of writing (e.g., journalism). Jim Meyer considers this a useful characteristic in explaining the use of the term to mean published material in a particular field (e.g., "scientific literature"), as such writing must use language according to particular standards. The problem with the formalist definition is that in order to say that literature deviates from ordinary uses of language, those uses must first be identified; this is difficult because "ordinary language" is an unstable category, differing according to social categories and across history.
What is the difficulty with "ordinary language" according to cultural categories?
A:
unanswerable