Question: Meanwhile, Kerry's staff began their own investigations and, on October 14, issued a report that exposed illegal activities on the part of Lieutenant Colonel Oliver North, who had set up a private network involving the National Security Council and the CIA to deliver military equipment to right-wing Nicaraguan rebels (Contras). In effect, North and certain members of the President's administration were accused by Kerry's report of illegally funding and supplying armed militants without the authorization of Congress. Kerry's staff investigation, based on a year-long inquiry and interviews with fifty unnamed sources, is said to raise "serious questions about whether the United States has abided by the law in its handling of the contras over the past three years."
Try to answer this question if possible: Who were the Contras?
Answer: right-wing Nicaraguan rebels
Question: Most fatty acids are non-essential, meaning the body can produce them as needed, generally from other fatty acids and always by expending energy to do so. However, in humans, at least two fatty acids are essential and must be included in the diet. An appropriate balance of essential fatty acids—omega-3 and omega-6 fatty acids—seems also important for health, although definitive experimental demonstration has been elusive. Both of these "omega" long-chain polyunsaturated fatty acids are substrates for a class of eicosanoids known as prostaglandins, which have roles throughout the human body. They are hormones, in some respects. The omega-3 eicosapentaenoic acid (EPA), which can be made in the human body from the omega-3 essential fatty acid alpha-linolenic acid (ALA), or taken in through marine food sources, serves as a building block for series 3 prostaglandins (e.g., weakly inflammatory PGE3). The omega-6 dihomo-gamma-linolenic acid (DGLA) serves as a building block for series 1 prostaglandins (e.g. anti-inflammatory PGE1), whereas arachidonic acid (AA) serves as a building block for series 2 prostaglandins (e.g. pro-inflammatory PGE 2). Both DGLA and AA can be made from the omega-6 linoleic acid (LA) in the human body, or can be taken in directly through food. An appropriately balanced intake of omega-3 and omega-6 partly determines the relative production of different prostaglandins, which is one reason why a balance between omega-3 and omega-6 is believed important for cardiovascular health. In industrialized societies, people typically consume large amounts of processed vegetable oils, which have reduced amounts of the essential fatty acids along with too much of omega-6 fatty acids relative to omega-3 fatty acids.
Try to answer this question if possible: At least how many fatty acids are essential to the human health and have to be consumed rather than produced by the body?
Answer: two
Question: Hong Taiji's bureaucracy was staffed with many Han Chinese, including many newly surrendered Ming officials. The Manchus' continued dominance was ensured by an ethnic quota for top bureaucratic appointments. Hong Taiji's reign also saw a fundamental change of policy towards his Han Chinese subjects. Nurhaci had treated Han in Liaodong differently according to how much grain they had, those with less than 5 to 7 sin were treated like chattel while those with more than that amount were rewarded with property. Due to a revolt by Han in Liaodong in 1623, Nurhachi, who previously gave concessions to conquered Han subjects in Liaodong, turned against them and ordered that they no longer be trusted; He enacted discriminatory policies and killings against them, while ordering that Han who assimilated to the Jurchen (in Jilin) before 1619 be treated equally as Jurchens were and not like the conquered Han in Liaodong. Hong Taiji instead incorporated them into the Jurchen "nation" as full (if not first-class) citizens, obligated to provide military service. By 1648, less than one-sixth of the bannermen were of Manchu ancestry. This change of policy not only increased Hong Taiji's manpower and reduced his military dependence on banners not under his personal control, it also greatly encouraged other Han Chinese subjects of the Ming dynasty to surrender and accept Jurchen rule when they were defeated militarily. Through these and other measures Hong Taiji was able to centralize power unto the office of the Khan, which in the long run prevented the Jurchen federation from fragmenting after his death.
Try to answer this question if possible: What proportion of bannerman were Manchu by 1648?
Answer: one-sixth
Question: The current–voltage characteristic of an LED is similar to other diodes, in that the current is dependent exponentially on the voltage (see Shockley diode equation). This means that a small change in voltage can cause a large change in current. If the applied voltage exceeds the LED's forward voltage drop by a small amount, the current rating may be exceeded by a large amount, potentially damaging or destroying the LED. The typical solution is to use constant-current power supplies to keep the current below the LED's maximum current rating. Since most common power sources (batteries, mains) are constant-voltage sources, most LED fixtures must include a power converter, at least a current-limiting resistor. However, the high resistance of three-volt coin cells combined with the high differential resistance of nitride-based LEDs makes it possible to power such an LED from such a coin cell without an external resistor.
Try to answer this question if possible:  What feature do no LED fixtures need to have?
Answer:
unanswerable