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: After a new wave of UN sanctions, on 11 March 2013, North Korea claimed that it had invalidated the 1953 armistice. On 13 March 2013, North Korea confirmed it ended the 1953 Armistice and declared North Korea "is not restrained by the North-South declaration on non-aggression". On 30 March 2013, North Korea stated that it had entered a "state of war" with South Korea and declared that "The long-standing situation of the Korean peninsula being neither at peace nor at war is finally over". Speaking on 4 April 2013, the U.S. Secretary of Defense, Chuck Hagel, informed the press that Pyongyang had "formally informed" the Pentagon that it had "ratified" the potential usage of a nuclear weapon against South Korea, Japan and the United States of America, including Guam and Hawaii. Hagel also stated that the United States would deploy the Terminal High Altitude Area Defense anti-ballistic missile system to Guam, because of a credible and realistic nuclear threat from North Korea. Question: How does the United States view North Korea's threats?
answer:
credible and realistic nuclear threat

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Passage: Dismayed to find that groundbreaking work had already been undertaken by Helmholtz who had conveyed vowel sounds by means of a similar tuning fork "contraption", he pored over the German scientist's book. Working from his own erroneous mistranslation of a French edition, Bell fortuitously then made a deduction that would be the underpinning of all his future work on transmitting sound, reporting: "Without knowing much about the subject, it seemed to me that if vowel sounds could be produced by electrical means, so could consonants, so could articulate speech." He also later remarked: "I thought that Helmholtz had done it ... and that my failure was due only to my ignorance of electricity. It was a valuable blunder ... If I had been able to read German in those days, I might never have commenced my experiments!"[N 7] Question: By what means did Bell conclude vowel sounds could be made?
answer:
electrical

question:
Passage: Ion gauges are used in ultrahigh vacuum. They come in two types: hot cathode and cold cathode. In the hot cathode version an electrically heated filament produces an electron beam. The electrons travel through the gauge and ionize gas molecules around them. The resulting ions are collected at a negative electrode. The current depends on the number of ions, which depends on the pressure in the gauge. Hot cathode gauges are accurate from 103 torr to 1010 torr. The principle behind cold cathode version is the same, except that electrons are produced in a discharge created by a high voltage electrical discharge. Cold cathode gauges are accurate from 102 torr to 109 torr. Ionization gauge calibration is very sensitive to construction geometry, chemical composition of gases being measured, corrosion and surface deposits. Their calibration can be invalidated by activation at atmospheric pressure or low vacuum. The composition of gases at high vacuums will usually be unpredictable, so a mass spectrometer must be used in conjunction with the ionization gauge for accurate measurement. Question: What gauge is accurate from 10-2 torr to 10-9 torr?
answer:
Cold cathode gauges