for electromagnetic activity
对于电磁活动
以上为机器翻译结果，长、整句建议使用 人工翻译 。
We can find out that from 2 meters to 20 meters is a difficulty for the several mainly electromagnetic methods, but this domain is closed related with human's activity.
由此可见，地下2～20米范围对于以上几种方法来说都是一个困难，而这一范围却与人类活动极为密切。
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