Initial marketing activities were based on the expansion of______.

A．It is marked by a compulsive craving for drags,
B．It can cause a wide variety of mental reactions.
C．It can make people commit crimes.
D．It is not difficult to be off the habit.

A．Because the anti-piracy protection has been granted to some films.
B．Because the system cannot comply with high-quality DVD player.
C．Because the system may need additional equipment for proper operation.
D．Because there is flaw in its design.