I know that the answer to the question "What unit of measure is used to measure smog" is in "A dense wave of smog began in the Central and Eastern part of China on 2 December 2013 across a distance of around 1,200 kilometres (750 mi), including Tianjin, Hebei, Shandong, Jiangsu, Anhui, Shanghai and Zhejiang. A lack of cold air flow, combined with slow-moving air masses carrying industrial emissions, collected airborne pollutants to form a thick layer of smog over the region. The heavy smog heavily polluted central and southern Jiangsu Province, especially in and around Nanjing, with its AQI pollution Index at "severely polluted" for five straight days and "heavily polluted" for nine. On 3 December 2013, levels of PM2.5 particulate matter average over 943 micrograms per cubic metre, falling to over 338 micrograms per cubic metre on 4 December 2013. Between 3:00 pm, 3 December and 2:00pm, 4 December local time, several expressways from Nanjing to other Jiangsu cities were closed, stranding dozens of passenger buses in Zhongyangmen bus station. From 5 to 6 December, Nanjing issued a red alert for air pollution and closed down all kindergarten through middle schools. Children's Hospital outpatient services increased by 33 percent; general incidence of bronchitis, pneumonia, upper respiratory tract infections significantly increased. The smog dissipated 12 December. Officials blamed the dense pollution on lack of wind, automobile exhaust emissions under low air pressure, and coal-powered district heating system in North China region. Prevailing winds blew low-hanging air masses of factory emissions (mostly SO2) towards China's east coast.". Can you tell me what it is?
Ans: micrograms per cubic metre

I know that the answer to the question "what is the first group mentioned?" is in "During the 16th and 17th centuries slave traders began to raid the region as part of the expansion of the Saharan and Nile River slave routes. Their captives were slaved and shipped to the Mediterranean coast, Europe, Arabia, the Western Hemisphere, or to the slave ports and factories along the West and North Africa or South the Ubanqui and Congo rivers. In the mid 19th century, the Bobangi people became major slave traders and sold their captives to the Americas using the Ubangi river to reach the coast. During the 18th century Bandia-Nzakara peoples established the Bangassou Kingdom along the Ubangi River.". Can you tell me what it is?
Ans: slave traders

I know that the answer to the question "What are these labels referred to as that seems like a dig to lower the reputation of such options?" is in "During the initial punk era, a variety of entrepreneurs interested in local punk-influenced music scenes began founding independent record labels, including Rough Trade (founded by record shop owner Geoff Travis) and Factory (founded by Manchester-based television personality Tony Wilson). By 1977, groups began pointedly pursuing methods of releasing music independently , an idea disseminated in particular by the Buzzcocks' release of their Spiral Scratch EP on their own label as well as the self-released 1977 singles of Desperate Bicycles. These DIY imperatives would help form the production and distribution infrastructure of post-punk and the indie music scene that later blossomed in the mid-1980s.". Can you tell me what it is?
Ans: DIY imperatives

I know that the answer to the question "If a class is a proper class what can it not be?" is in "The second approach to the problem took as its base the notion of class, and defines a set as a class which belongs to other classes, while a proper class is defined as a class which does not belong to other classes. Under the ZermeloFraenkel approach, the axioms impede the construction of a set of all sets which do not belong to themselves. In contrast, under the von Neumann approach, the class of all sets which do not belong to themselves can be constructed, but it is a proper class and not a set.". Can you tell me what it is?
Ans: set