It is ________ the customers’ needs that has made chain stores so popular in big cities in China.

A．meeting

B．met

C．to have met

D．being met

使血液沿单方向流动的基础是( )。

A．心脏特殊传导组织的节律性活动

B．大动脉的弹性

C．心瓣膜的规律性开闭活动

D．骨骼肌活动和胸内负压促进静脉回流

E．以上都不是