Various natural disasters occurred frequently in Jianghan Basin during the Song and Yuan period, among which both the droughts and flood disasters had the highest frequency and the biggest influence.

宋元时期江汉平原各种自然灾害频发，其中水旱灾害的发生频率最高、产生影响最大。

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Dust events occurred frequently in Beijing in recent years.

近年来，北京频繁发生沙尘天气。

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Systemic complications occurred frequently in liver, kidney, lung, and heart.

并发症多累及肝、肾、肺、心。

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You may be referred to a specialist in ear, nose and throat (ENT) disorders (otolaryngologist) if the problem has been persisting for some time, is not responding to treatment, or has occurred frequently.

CNN: Ear infection (middle ear)

This promotion frequently occurred in the past, but hardly fits the everyday-low-price mantra espoused by new CEO Ron Johnson.

FORBES: Another Sign CEO Johnson Can't Make Up His Mind About J.C. Penney

The results showed that the various technical patterns mostly occurred far more frequently than they would have done if they were truly random events.

ECONOMIST: Heads, shoulders and broadening bottoms | The