The correct answer is d.
A good example of an exchange using the specialist
system is the NYSE. Each stock listed on the NYSE
is allocated to a specialist and all buying and selling
of a stock occurs at the location of this person,
known as "the trading post." Buyers and
sellers represented by a floor trader will meet at
the trading post to learn about the best current bid
and ask price for a security. These bid and ask offers
are called out loud and indicate the current prices
to any interested party. A trade will be executed
when bid and ask orders meet.
specialist doesn't only meet up buyers and sellers.
Many specialists are forced to hold an inventory of
shares themselves to minimize the imbalance of buy
and sell orders. The specialist does this until a
equilibrium price is reached, i.e. when demand and
supply are very close. Buying an inventory of stocks
is not a common occurrence, it is estimated that a
specialist will be in on only 1 out of every 10-15