落后的英文是表达为backward, fall behind。
backward：
adj.向后的;朝后的;倒退的;反向的;落后的;进步缓慢的；
fall behind：落后;跟不上;不能按时完成（或交付）
相关介绍
It's bad to use such backward technique in basic industry.
将此落后的技术运用到基础工业中是有害的。
It is urgent to change this traditional and backward manufacturing technology.
这种传统落后的制造工艺急待改变。
Work hard, or you will fall behind the other students.
努力学习，否则你将落后于其他人。
She didn't fall behind the others in the study of English.
在英语学习上，她没有落后于别人。
A week's illness made her fall behind with her study.
得了一星期的病，她在学习上落后了。
