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.
The predetermined price the parties agree to buy and sell the asset for is known as the forward price. The specified time in the future -- which is when delivery and payment occur -- is known as the delivery date. Because it is a function of an underlying asset, a futures contract is a derivative product. Contracts are negotiated at futures exchanges, which act as a marketplace between buyers and sellers. The buyer of a contract is said to be long position holder, and the selling party is said to be short position holder.