There is little doubt, however, that desertification in most areas results primarily from human activities rather than natural processes.
然而，几乎毫无疑问，大多数地区的沙漠化主要是由于人类活动而不是自然过程造成的。
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When people engage in activities that help others, their brain releases endorphins, the brain's natural opiates, which induce in people a feeling of well-being.