可以不加冠词，例如：
1、The need to communicate is a key characteristic of human society.需要交流是人类社会最重要的一个特征。
2、Scientists continue to push back the boundaries of human knowledge.科学家不断扩大人类知识的范围。
3、The cost in terms of human life was high.付出了很大的生命代价。
可以不加冠词，例如：
1、The need to communicate is a key characteristic of human society.需要交流是人类社会最重要的一个特征。
2、Scientists continue to push back the boundaries of human knowledge.科学家不断扩大人类知识的范围。
3、The cost in terms of human life was high.付出了很大的生命代价。
