Answer:
A monopsony is market where there is only one buyer, e.g. the government is the sole buyer for nuclear submarines in the US.
The demand curve of a monopsony is similar to the demand curve of any other type of market, i.e. it is downward sloping. Since there is only 1 buyer, the demand curve is also the supply curve. If the monopsonist wants to increase the quantity demanded at a lower price, the supplier (or suppliers) must be able to lower its costs and that generally results in lower labor costs.
