下列选项中不属于理想化物理模型的是（　　）

A．电场

B．质点

C．点电荷

D．轻弹簧

18．—Jim, are you ______ this Saturday?

—Oh, sorry. I need to go to the bookshop _____ the bank on Saturday.

A．convenient; and

B．convenient; as well as

C．available; as well as

D．available; with