What you have done might do harm to other people.详细分析一下句子结构,哪是主谓宾
What is important is to learn English这句话也是主语从句只不过句型变了，这句话里面的两个is 和What you have done might do harm to other people这个句子里面的done和might在句子中的充当的作用是一样的。充当句子中的动词和谓语成分，