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.

Example Input: Passage: The word phonology comes from the Greek φωνή, phōnḗ, "voice, sound," and the suffix -logy (which is from Greek λόγος, lógos, "word, speech, subject of discussion"). Definitions of the term vary. Nikolai Trubetzkoy in Grundzüge 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?
Example Output: Nikolai Trubetzkoy

Example Input: Passage: According to the 2010 Census, whites made up 51% of Houston's population; 26% of the total population were non-Hispanic whites. Blacks or African Americans made up 25% of Houston's population. American Indians made up 0.7% of the population. Asians made up 6% (1.7% Vietnamese, 1.3% Chinese, 1.3% Indian, 0.9% Pakistani, 0.4% Filipino, 0.3% Korean, 0.1% Japanese), while Pacific Islanders made up 0.1%. Individuals from some other race made up 15.2% of the city's population, of which 0.2% were non-Hispanic. Individuals from two or more races made up 3.3% of the city. At the 2000 Census, there were 1,953,631 people and the population density was 3,371.7 people per square mile (1,301.8/km²). The racial makeup of the city was 49.3% White, 25.3% African American, 5.3% Asian, 0.7% American Indian, 0.1% Pacific Islander, 16.5% from some other race, and 3.1% from two or more races. In addition, Hispanics made up 37.4% of Houston's population while non-Hispanic whites made up 30.8%, down from 62.4% in 1970. Question: According to the 2000 census, what is the population of Houston?
Example Output: 1,953,631

Example Input: Passage: Stepper motors are a type of motor frequently used when precise rotations are required. In a stepper motor an internal rotor containing PMs or a magnetically soft rotor with salient poles is controlled by a set of external magnets that are switched electronically. A stepper motor may also be thought of as a cross between a DC electric motor and a rotary solenoid. As each coil is energized in turn, the rotor aligns itself with the magnetic field produced by the energized field winding. Unlike a synchronous motor, in its application, the stepper motor may not rotate continuously; instead, it "steps"—starts and then quickly stops again—from one position to the next as field windings are energized and de-energized in sequence. Depending on the sequence, the rotor may turn forwards or backwards, and it may change direction, stop, speed up or slow down arbitrarily at any time. Question: What do stepper motor rotors allign themselves with?
Example Output:
magnetic field produced by the energized field winding