Answer:
The correct answer is: when buyers and sellers have influence on price.
Explanation:
The imperfect market situations exist when there are few buyers or sellers such that they are able to influence the market. For instance, in a perfectly competitive market, there is a large number of buyers and sellers. So, any single buyer or seller is not able to influence the market. The price and output are determined by the market forces.
In an imperfect market such as monopoly or oligopoly, few firms exist so they are able to fix output and price on their own.