instruction:
This task is about writing a correct answer for the reading comprehension task. Based on the information provided in a given passage, you should identify the shortest continuous text span from the passage that serves as an answer to the given question. Avoid answers that are incorrect or provides incomplete justification for the question.
question:
Passage: The softness of copper partly explains its high electrical conductivity (59.6106 S/m) and thus also high thermal conductivity, which are the second highest (to silver) among pure metals at room temperature. This is because the resistivity to electron transport in metals at room temperature mostly originates from scattering of electrons on thermal vibrations of the lattice, which are relatively weak for a soft metal. The maximum permissible current density of copper in open air is approximately 3.1106 A/m2 of cross-sectional area, above which it begins to heat excessively. As with other metals, if copper is placed against another metal, galvanic corrosion will occur. Question: What is the explanation for copper's capacity for electrical conductivity?
answer:
The softness

question:
Passage: The word phonology comes from the Greek , phone, "voice, sound," and the suffix -logy (which is from Greek , logos, "word, speech, subject of discussion"). Definitions of the term vary. Nikolai Trubetzkoy in Grundzuge der Phonologie (1939) defines phonology as "the study of sound pertaining to the system of language," as opposed to phonetics, which is "the study of sound pertaining to the act of speech" (the distinction between language and speech being basically Saussure's distinction between langue and parole). More recently, Lass (1998) writes that phonology refers broadly to the subdiscipline of linguistics concerned with the sounds of language, while in more narrow terms, "phonology proper is concerned with the function, behavior and organization of sounds as linguistic items." According to Clark et al. (2007), it means the systematic use of sound to encode meaning in any spoken human language, or the field of linguistics studying this use. Question: Who in 1939 defined phonology?
answer:
Nikolai Trubetzkoy

question:
Passage: On 9 September the OKL appeared to be backing two strategies. Its round-the-clock bombing of London was an immediate attempt to force the British government to capitulate, but it was also striking at Britain's vital sea communications to achieve a victory through siege. Although the weather was poor, heavy raids took place that afternoon on the London suburbs and the airfield at Farnborough. The day's fighting cost Kesselring and Luftflotte 2 (Air Fleet 2) 24 aircraft, including 13 Bf 109s. Fighter Command lost 17 fighters and six pilots. Over the next few days weather was poor and the next main effort would not be made until 15 September 1940. Question: How many Bf 109s were lost?
answer:
13