first line of defense

• 第一道防线

first line of defense的用法和样例：

例句

1. The first line of defense against disaster is a backup of the data.
   备份的数据是应对灾难的第一道防线。
2. Traditionally, users usually adopt Firewall as their first line of defence.
   传统上，网络用户一般采用防火墙作为安全的第一道防线。