It's a thorny subject.

这是个棘手的问题。

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It is an thorny problem how to choose proper words as the subject of a sentence in Chinese-English translation.

在汉英翻译过程中，怎样选择适当的词语作句子的主语往往是一个棘手的问题。

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This debate has highlighted both a degree of consensus and a degree of continuing controversy within the thorny subject of the predictability of earthquakes.

在地震的可否预测性这个多棘手的问题上，这场辩论既突出了多数人意见的地位，也突出了继续论战的地位。

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It "nails the thorny subject of race relations with a bilious zest that takes one's breath away", wrote the Guardian's theatre critic Michael Billington, in an early review.

BBC: Author fury at blackface casting at German theatre

The explanations, particularly in the thorny field of quantum physics, are excellent, and the selection of subject matter skilfully winnows a vast field.

ECONOMIST: History of science: Time's arrow | The