regeneration under crown cover林冠下更新
tunnel under shallow cover浅埋隧道
under separate cover在另函中;另封;另邮;另函邮寄
under plain cover以普通信封寄发;用没有注明商号;翻译;没有注明寄发人姓名
under insurance cover根据保险涵盖;根据保险
under the cover遮盖着
under superficial cover冠冕堂皇
under r cover to附在信中
send under plain cover用不注明发信人姓名的封皮寄发
ADJ（形容词） Undercover work involves secretly obtaining information for the government or the police. 秘密的
...an undercover operation designed to catch drug smugglers.
…一次为抓捕毒品走私贩而策划的秘密行动。
ADV（副词） Undercover is also an adverb. 秘密地 [ADV after v]
Swanson persuaded Hubley to work undercover to capture the killer.
斯旺森说服了赫布利秘密工作以捕获凶手。