谁说不能做谓语?be to do既定长久计划/be about to do既定计划即可实现/be going to do临时计划打算/used to do过去有现在无的习惯/ought to do按理应该/have to do被迫无奈不得不,这些都是合成谓语.只是to do不能单独做谓语而已.
主语：To understand English is not a difficult thing.
宾语：I want to learn English well.
主补：My job is to teacher English.
宾补：He asked me to teach him English.
定语：I have lots of books to read.
状语：Let's stop to have a rest.