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.
Commodity broker. A commodity broker is a firm or individual who executes orders to buy or sell commodity contracts on behalf of clients and charges them a commission. A firm or individual who trades for his own account is called a trader. Commodity contracts include futures, options, and similar financial derivatives. Clients who trade commodity contracts are either hedgers using the derivatives markets to manage risk, or speculators who are willing to assume that risk from hedgers in hopes of a profit.