There Are Two Firms in an Industry, Firm a and Firm

There are two firms in an industry, Firm A and Firm B. Both firms sell a homogenous product. If one firm sets a price higher than the other firm, then all the demand goes to the firm setting the lower price. If prices are equal, the demand is shared equally between the two firms. The following figure depicts the demand faced by Firm A. What is Firm B's strategy that could explain such a demand curve faced by Firm A?

A) Firm B sets its price to p.
B) Firm B sets its price to p'.
C) Firm B equates Firm A's price for any price between p and p' and never sets a price outside this interval.
D) Firm B sets its price to p' whenever the price of Firm A is greater than p, and sets a price equal to Firm A's whenever Firm A sets its price below p.