ace in the hole 密藏的王牌（備而未用的王牌）；應急的手段；可共患難的朋友；黑馬

例句：

Myfamily's ace in the hole is its popular relative, Ancestry.com. Both sites are owned by parent company, Generations Network Inc., which means that Ancestry's wealth of digitally scanned data and genealogy research can be linked to myfamily.com, enriching the site. Another big plus for myfamily is that it gives users the chance to add voice recordings to photos. These can be used to narrate a slide show (called SnapGenies) or when commenting on a shared image. Voice comments are added by following on-screen instructions and calling a 1-800 number.（摘自網絡化身家庭餐桌，《華爾街日報》中文網絡版，2007/11/05）

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