下列关于杠杆的说法中，正确的是[ ]

A．杠杆只可以是直的

B．杠杆一定有支点

C．杠杆的支点可以不在杠杆上

D．杠杆的长度等于动力臂与阻力臂之和

A word processor enables you to create a (66) ., store it electronically on a disk, display it on a screen, modify it by entering commands and characters from the keyboard, and print it on a printer.

A．file

B．document

C．text

D．paper