只讲解这三个单词做动词的用法如下：
1.require
1）require sth (of sb)
2）require sb to do sth
3）require doing 主动表被动
4）require that-clause〔虚拟语气：(should)+V原〕
2.demand
1）demand sth of/from sb
2）demand to do sth；demand to be done
3）demand that-clause〔虚拟语气：(should)+V原〕
3.request
1）request sth of/from sb
2）request sb to do sth
3）request that-clause〔虚拟语气：(should)+V原〕