a) It's caused by bacteria. Pericoronitis is an infection. It's caused by normal oral bacteria, like those found in dental plaque. It's the gum relationship around a partially-erupted tooth that allows pericoronitis to occur.
A futures exchange or futures market is a central financial exchange where people can trade standardized futures contracts; that is, a contract to buy specific quantities of a commodity or financial instrument at a specified price with delivery set at a specified time in the future. These types of contracts fall into the category of derivatives. The opposite of the futures market is the spots market, where trades will occur immediately (2 business days) after a transaction agreement has been made, rather than at a predetermined time in the future.
One feature of futures trading is the ability to conduct transactions at almost any time of day. Commodity and futures markets are closed on weekends, but most futures contracts start trading on Sunday afternoon to start the week. Futures cover a wide range of asset classes, from agricultural commodities to energy products to stocks, and different commodities or financial products will keep different trading hours.