The most important thing about ancient civilizations is ____ part that they played in ____ history.

A．不填; 不填

B．a; the

C．the; the

D．the; 不填

关于动脉血的描述，正确的是（　　）

A．动脉中流动的血

B．血浆中含丰富养料的血

C．体循环中流动的血

D．血红蛋白与氧结合，颜色鲜红的血