They are more common in summer than in winter, and difficult to predict.

这种情况在夏天比冬天更常见，也很难预测。

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Currencies are notoriously volatile and difficult to predict. Even investment Banks with their armies of analysts frequently call it wrong.

货币的不稳定性和难预测性是众所周知的，就连投资银行和它们的分析师军团，也常常会出现误判的哦。

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In production process, many complex factors which influence cost affect each other and the coupling phenomenon exists, so it is important and difficult to predict the cost.

在生产过程中，影响产品成本的因素多而复杂，因素之间相互影响，存在耦合现象，因此准确预测成本是一个重要又难以解决的问题。

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"If the current posture of the Israeli government on Gaza continues it would not be difficult to predict that Turkish and Israeli relations will continue to be difficult and fragile,"

VOA: standard.2009.10.27

Mr Colley described market conditions in the UK as "extremely challenging" and difficult to predict.

BBC: Stirling firm Superglass installs new production line

Aside from adding an ugly dimension to the charred economic landscape, its effects would also be widespread and difficult to predict.

FORBES: Federal Reserve

Weather is inherently uncontrollable and difficult to predict, notes Dirnagl, but it is part and parcel of operating in the air emergency transport business.

FORBES: Air Methods: No. 1 Air Medical Emergency Service Provider Attracts Big Investors