Consider the Following Characteristics

Consider the following characteristics:
a.a market structure with barriers to entry
b.demand curves that are easily identified
c.firm cannot make zero profits in the long run
d.firm can reap long-run profits.
Which of the characteristics in the list above are shared by an oligopolist and a monopolist?

A) a, b, c and d
B) a, b and d
C) a, c and d
D) a and d