当人们非常密集地生活在一起，被传染的病人咳嗽或打喷嚏的时候，麻疹、腮腺炎和风疹病毒就很容易传播开来。
When people live close together, measles, mumps, and rubella viruses are more easily spread when an infected person coughs or sneezes.
密集的正地闪也与强回波区相对应，而稀疏的正地闪则多发生在系统后部的稳定性降水或云砧部位。
Moreover, the dense positive CG flashes can also be observed in the strong echo region, while sparse ones are in the weak and stable echo region or cloud anvil in the rear MCS.
在密集使用区-使用现存步道及营地-以一列行走步道，即使湿地或泥泞地。
In popular areas: - Concentrate use on existing trails and campsites. - Walk single file in the middle of the trail, even when wet or muddy.
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