One tool that is useful during both analysis and design is the （）,which is a pictorial representation of the items of information(entities) within the system and the relationships between these pieces of information.

A.data dictionary

B.dataflow diagram

C.use case diagram

D.entity-relation ship diagram

公安机关的职责是由公安机关的( )所决定的。

A．宗旨

B．任务

C．性质

D．职能