Problem: Extract the answer to the question from the following context. Question: A QED vacuum is a theoretical Hilbert space defined in what quantum mechanics theory? Context: In quantum mechanics and quantum field theory, the vacuum is defined as the state (that is, the solution to the equations of the theory) with the lowest possible energy (the ground state of the Hilbert space). In quantum electrodynamics this vacuum is referred to as 'QED vacuum' to distinguish it from the vacuum of quantum chromodynamics, denoted as QCD vacuum. QED vacuum is a state with no matter particles (hence the name), and also no photons. As described above, this state is impossible to achieve experimentally. (Even if every matter particle could somehow be removed from a volume, it would be impossible to eliminate all the blackbody photons.) Nonetheless, it provides a good model for realizable vacuum, and agrees with a number of experimental observations as described next.

A: quantum electrodynamics

Problem: Extract the answer to the question from the following context. Question: What property of a metal mixture has the letter R as the third letter? Context: Iron is usually found as iron ore on Earth, except for one deposit of native iron in Greenland, which was used by the Inuit people. Native copper, however, was found worldwide, along with silver, gold and platinum, which were also used to make tools, jewelry, and other objects since Neolithic times. Copper was the hardest of these metals, and the most widely distributed. It became one of the most important metals to the ancients. Eventually, humans learned to smelt metals such as copper and tin from ore, and, around 2500 BC, began alloying the two metals to form bronze, which is much harder than its ingredients. Tin was rare, however, being found mostly in Great Britain. In the Middle East, people began alloying copper with zinc to form brass. Ancient civilizations took into account the mixture and the various properties it produced, such as hardness, toughness and melting point, under various conditions of temperature and work hardening, developing much of the information contained in modern alloy phase diagrams. Arrowheads from the Chinese Qin dynasty (around 200 BC) were often constructed with a hard bronze-head, but a softer bronze-tang, combining the alloys to prevent both dulling and breaking during use.

A: hardness

Problem: Extract the answer to the question from the following context. Question: What do Catholics call their worship service? Context: When not celebrating Mass but still serving a liturgical function, such as the semiannual Urbi et Orbi papal blessing, some Papal Masses and some events at Ecumenical Councils, cardinal deacons can be recognized by the dalmatics they would don with the simple white mitre (so called mitra simplex).

A: Mass

Problem: Extract the answer to the question from the following context. Question: What is Tito's nationality? Context: Josip Broz Tito received a total of 119 awards and decorations from 60 countries around the world (59 countries and Yugoslavia). 21 decorations were from Yugoslavia itself, 18 having been awarded once, and the Order of the National Hero on three occasions. Of the 98 international awards and decorations, 92 were received once, and three on two occasions (Order of the White Lion, Polonia Restituta, and Karl Marx). The most notable awards included the French Legion of Honour and National Order of Merit, the British Order of the Bath, the Soviet Order of Lenin, the Japanese Order of the Chrysanthemum, the German Federal Cross of Merit, and the Order of Merit of Italy.

A:
Yugoslavia