Nearly all the illegal drug heroin in the United States come through ______.

A．The State Department regards Iran, Syria, Nigeria and Burma as the countries which sell and produce illegal drugs.
B．In its yearly report, the State Department failed to mention international illegal control.
C．The United States possesses the largest amount of heroin in the world.
D．Nigeria is the biggest country involved in illegal drug sales around the world.

A．To set up a joint research center.
B．To extend their cooperation.
C．To hire some researchers.
D．To complete the project.