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Although an alloy is technically an impure metal, when referring to alloys, the term "impurities" usually denotes those elements which are not desired. These impurities are often found in the base metals or the solutes, but they may also be introduced during the alloying process. For instance, sulfur is a common impurity in steel. Sulfur combines readily with iron to form iron sulfide, which is very brittle, creating weak spots in the steel. Lithium, sodium and calcium are common impurities in aluminium alloys, which can have adverse effects on the structural integrity of castings. Conversely, otherwise pure-metals that simply contain unwanted impurities are often called "impure metals" and are not usually referred to as alloys. Oxygen, present in the air, readily combines with most metals to form metal oxides; especially at higher temperatures encountered during alloying. Great care is often taken during the alloying process to remove excess impurities, using fluxes, chemical additives, or other methods of extractive metallurgy.

What are the three common impurities in aluminum alloys?
Answer: Lithium, sodium and calcium
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Dowding accepted that as AOC, he was responsible for the day and night defence of Britain, and the blame, should he fail, would be laid at his door. When urgent changes and improvements needed to be made, Dowding seemed reluctant to act quickly. The Air Staff felt that this was due to his stubborn nature and reluctance to cooperate. Dowding's opponents in the Air Ministry, already critical of his handling of the day battle (see Battle of Britain Day and the Big Wing controversy), were ready to use these failings as a cudgel with which to attack him and his abilities.

Who thought Dowding was stubborn and didn't like to cooperate?
Answer: Air Staff
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Translations of sung texts—whether of the above type meant to be sung or of a more or less literal type meant to be read—are also used as aids to audiences, singers and conductors, when a work is being sung in a language not known to them. The most familiar types are translations presented as subtitles or surtitles projected during opera performances, those inserted into concert programs, and those that accompany commercial audio CDs of vocal music. In addition, professional and amateur singers often sing works in languages they do not know (or do not know well), and translations are then used to enable them to understand the meaning of the words they are singing.

Who can translations of a sung text aid?
Answer:
audiences, singers and conductors