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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The situation of safety production is severe and very serious accidents occurred frequently.

安全生产形势严峻，重特大事故频发。

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Willow twig gall midge( Rhabdophaga salics Schrank) occurred frequently and caused heavy loss.

杞柳瘿蚊发生频繁，造成很大的损失。

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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