做助动词:疑问句：把have提前，如Have you been there before? Have you done your homework?否定句，变have为haven't 。情态动词疑问句：用Do提问，如Do you have to do this right now? Does Tom have to go to school?否定句：加don't，如I don't have to do it now.Tom doesn't have to go to school today. 做“有”讲的时候，和一般动词用法相同。