To keep a conversation flowing smoothly, it is better for the participants______

A．Iran has the technology of producing Scud missile
B．some countries could send long-range missile right after they decide to do so
C．Iraq can not become a missile threat to America now
D．both A and C

A．of extreme importance in expressing feelings and exchanging ideas
B．something through which one can see a person's inner world
C．of considerable significance in making conversations interesting
D．something the value of which is largely a matter of long debate