"clandestine intelligence operations"
"cloak-and-dagger activities behind enemy lines"
"hole-and-corner intrigue"
"secret missions"
"a secret agent"
"secret sales of arms"
"surreptitious mobilization of troops"
"an undercover investigation"
"underground resistance"
来自《简明英汉词典》
来自《现代英汉综合大词典》
来自辞典例句
来自辞典例句
来自辞典例句