the act of keeping a secret watch for intelligence purposes
同义词：spying
One works undercover, reporting from the entourage of a drug lord (Eric Tsang).
NEWYORKER: Infernal Affairs
英汉双解词典包含3185865条英汉词条，基本涵盖了全部常用单词的翻译及用法，是英语学习的有利工具。