One of the Reasons Cartels Are Considered Unstable Is That

One of the reasons cartels are considered unstable is that

A) it is inefficient to manage individual firms collectively.
B) consumers seek out substitutes to the cartel product.
C) there are wide fluctuations in price as cartel members vary their output.
D) individual members of the cartel have an incentive to violate the cartel agreement.
E) member firms reduce their investment,thereby becoming uncompetitive over time.