His signature is difficult to imitate.

他的签名很难模仿。

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Core competencies are abilities that contribute to excellence and are difficult to imitate.

核心竞争力是指那些成就卓越而又很难模仿的能力。

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Smoking was deemed safe for decades, as laboratories found it difficult to imitate smoking-related cancer in animals.

因为实验研究发现人类所患的与吸烟有关的癌症难以在动物身上仿效，几十年来抽烟被认为是安全的。

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Is something about it scarce and difficult to imitate?

FORBES: Why Leaders Stopped Caring About Strategy -- and How They Can Reclaim It

With its new chemical composition and color-shifting ink, the Series 1996 was an incredibly difficult bill to imitate successfully.

FORBES: Book Review