PPT最后一页写“back up“是往后退的意思，back up的意思有：支持，<篮球>协防，补防，堵塞，复制，往后退。
back up
1、Radio signals received from the galaxy's centre back up the black hole theory
从该星系中心收到的无线电信号证实了黑洞理论。
2、Make a point of backing up your files at regular intervals
一定要定期备份文件。
3、The Secretary General says the declaration must now be backed up by concrete and effective actions
秘书长说现在必须将宣言付诸具体有效的行动。
4、His employers, Norfolk social services, backed him up.
他的雇主——诺福克社会服务中心给予了他支持。
5、The girl denied being there, and the man backed her up.
女孩否认在场，那名男子证实了她的话。
6、Back up, Hans
倒车，汉斯。
7、Traffic into London on the M11 was backed up for several miles.
进入伦敦的车辆在11号高速公路上堵了好几英里。
8、I backed up carefully until I felt the wall against my back
我小心翼翼地后退，直到感觉后背碰到了墙壁。
9、I get so annoyed when I lose work because I've forgotten to back it up.
当我因为忘了备份把完成的工作弄丢时，真是懊恼极了。
10、It is time the Government backed up its advert campaigns with tougher measures.
是政府采取更严厉的措施来兑现其宣传承诺的时候了。