Monopolistic Competition Means That

Monopolistic competition means that

A) firms are in a monopoly,but they compete.
B) firms are in perfect competition,but they collude similar to monopolies.
C) firms differentiate their output,which makes them price makers,but barriers to entry are low or nonexistent.
D) oligopoly firms collude until they become monopolies.
E) firms have downward-sloping demand.