Due to a long period of separation from their family members, these "left-behind" people in far-flung underdeveloped regions have suffered certain psychological problems to some extent.
由于家庭成员长期分离，这些广泛分布于不发达地区的留守人口都有一定程度的心理问题。
Jigging washing will be one of the major coal separation methods during a long period both at present and in the future.
在现阶段乃至今后相当长的时期内跳汰选仍将是主要选煤方法之一。
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