Which of the Following Is TRUE

Which of the following is TRUE?

A) In both perfect competition and oligopoly, the strategic dependence of the firms means that none can earn positive economic profits.
B) Whether firms in an industry can consistently earn positive economic profits depends on whether there are barriers to the entry of new firms.
C) A duopoly arises when firms engage in a price war.
D) An oligopoly arises when one firm can lower its cost below those of its competitors.