Defense Condition National Defense Alert Status的用法和樣例：
例句
They have put the army on the alert. 他們已使軍隊進(jìn)入戒備狀態(tài)。
These networks are on the alert for warning signs that show the weakening of rock layers that can precede an earthquake. 這些網(wǎng)絡(luò )始終處于戒備狀態(tài)，搜索地震前巖石可能松動(dòng)的警告跡象。
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