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An analysis of two sandstorms in spring 1990 .

1990年春季两次沙尘暴特征分析。

Northern china hit by worst sandstorms in years .

中国北部受多年来最严重的沙暴袭击。

It is believed by many people to have been gradually covered over by sandstorms .

许多人相信它已逐渐被风沙所覆盖。

The government has planted millions of trees around the city as a barrier against desert sandstorms .

政府在城市周边种植了上百万棵树木，以阻挡沙尘。

Sandstorms occur when strong winds hit desert areas , whipping up the top layer of sand .

沙尘暴的发生是由于强风吹袭沙漠表面，掀起了最上层的沙子。