Which one is WRONG about the pericardium （）.

A．It is located in the middle mediastinum

B．It can be divided into fibrous and serous pericardium

C．It encloses the heart

D．It forms a closed cavity called pericardial cavity

E．It attaches to the visceral pleura

确定系统边界属于数据库设计的（）阶段。

A．需求分析 

B．概念设计 

C．逻辑设计 

D．物理设计