Oligopolistic industries are characterized by:
1. a few dominant firms and substantial entry barriers.
2. a few dominant firms and no barriers to entry.
3. a large number of firms and low entry barriers.
4. a few dominant firms and low entry barriers.

1. a few dominant firms and substantial entry barriers.

Explanation:

An industry dominated by a few large suppliers is known as Oligopolistic industries.Often an oligopoly is defined as an industry with 2 or more but not more than 20  suppliers.

Since there may be a monopoly under oligopoly, the existing firms create artificial  barriers to new entry. For example, economies of scale are important entry  barriers in a number of oligopolistic industries such as the aircraft, rubber and  cement industries. In these industries, each of the existing say three or four firms  might have sufficient sales to achieve economies of scale.

So based on the above discussion answer is 1. a few dominant firms and substantial entry barriers.

answer(b) revenue account which increases;