Even the smoking-lung cancer connection took decades of epidemiological head-scratching to figure out.

尽管吸烟能导致肺癌这个令人挠头的难题也是经历了数十年的探索才最终得出了结论。

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We've all had a few head-scratching moments with generics, but far and away the trickiest part of generics is wildcards.

对于泛型我们都经历过一些痛苦的回忆，但毫无疑问通配符是最棘手的部分。

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In a world besotted with gadgetry, few consumer products have generated as much excitement - and head-scratching - as high-definition television.

在这个到处都被小玩意冲昏头脑的世界里，很少有消费品像高清晰电视一样让人激动人心同时又令人哭笑不得。

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"The build was completed with lots of head-scratching and weekend work, " the company said.

BBC: Zipwhip's Textpresso

Also head-scratching: The government is perpetually trying to figure out how to make Social Security long-term solvent.

FORBES: Retirement Caps and Budget Politics

There's a degree of head-scratching going on about why this is the ideal candidate for this particular role.

BBC: The new CG and some raised eyebrows