1. The police worked under cover to gather information.
警方秘密行动以收集信息。

2. He moved under cover of darkness to avoid being seen.
他在黑暗掩护下移动以避免被发现。

3. The journalist was working under cover for a long investigation.
该记者进行长期卧底调查。

4. They escaped under cover of night.
他们在夜幕掩护下逃离。

A: How did they enter the building unnoticed?
A：他们是怎么不被注意地进入大楼的？

B: They went under cover of darkness.
B：他们在黑暗掩护下进入的。

1) 指在隐蔽或秘密状态下进行的行动

2) 指在某种环境掩护下进行的行为

3) 常用于描述调查或行动中的隐蔽方式

1. 在掩护下；秘密地进行

e.g. They worked under cover to avoid detection.
他们秘密工作以避免被发现。

2. 在（黑暗、夜晚等）掩护下

e.g. He escaped under cover of night.
他在夜幕掩护下逃走。

noun/adverb phrase

1. In a hidden or secret way, often to avoid being seen or detected.

Synonym: covertly, secretly, clandestinely