Problem: Electric instruments such as the electric guitar, the electric bass and the ondes Martenot appear occasionally in the classical music of the 20th and 21st centuries. Both classical and popular musicians have experimented in recent decades with electronic instruments such as the synthesizer, electric and digital techniques such as the use of sampled or computer-generated sounds, and instruments from other cultures such as the gamelan.
What type of musicians besides classical have experimented with electronic instruments?
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Answer: popular

Problem: When comparing different documents, or "witnesses", of a single, original text, the observed differences are called variant readings, or simply variants or readings. It is not always apparent which single variant represents the author's original work. The process of textual criticism seeks to explain how each variant may have entered the text, either by accident (duplication or omission) or intention (harmonization or censorship), as scribes or supervisors transmitted the original author's text by copying it. The textual critic's task, therefore, is to sort through the variants, eliminating those most likely to be un-original, hence establishing a "critical text", or critical edition, that is intended to best approximate the original. At the same time, the critical text should document variant readings, so the relation of extant witnesses to the reconstructed original is apparent to a reader of the critical edition. In establishing the critical text, the textual critic considers both "external" evidence (the age, provenance, and affiliation of each witness) and "internal" or "physical" considerations (what the author and scribes, or printers, were likely to have done).
How or why do variations enter a witness text?
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Answer: either by accident (duplication or omission) or intention (harmonization or censorship)

Problem: He attained a perfect score on the graduate school entrance exams to Princeton University in mathematics and physicsan unprecedented featbut did rather poorly on the history and English portions. Attendees at Feynman's first seminar included Albert Einstein, Wolfgang Pauli, and John von Neumann. He received a PhD from Princeton in 1942; his thesis advisor was John Archibald Wheeler. Feynman's thesis applied the principle of stationary action to problems of quantum mechanics, inspired by a desire to quantize the WheelerFeynman absorber theory of electrodynamics, laying the groundwork for the "path integral" approach and Feynman diagrams, and was titled "The Principle of Least Action in Quantum Mechanics".
When did he receive his PhD?
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Answer:
1942