deadly serious.

• 极其严重

deadly serious.的用法和样例：

例句

1. Its consequences were so serious that they are still being felt today.
   它的后果极其严重，直到现在还在发生影响。
2. In this special situation,our change in strategy was an extremely serious one.
   我们的战略转变，是在这些特殊情况之下进行的一个极其严重的转变。