[译] 他们警告过我们这种严重的形势。
[误] They warned us the serious situation.

[正] They warned us of/about the serious situation.
[注] warn 动词后可以接 of/about 短语，表示“告诫某人某种情况”的存在。还可以接介词 against 构成的短语，表示警告某人不要做某事，此时还可以用不定式短语表达。