warn sb to do sth提醒某人做某事
warn sb.not to do sth...警告某人不要做某事
网上有这个题目的：
3）Mrs.Smith warned her daughter ___ after drinking.
A.never to drive B.to never driver
C.never driving D.never drive
答案：A.warn sb to do sth.的否定形式为warn sb not to do sth.此处用的是否定词never.