do,does和did都是助动词，后接动词原形do和does一般用于现在时，do用于第一、第二人称；当主语是第三人称时就要把do改为does例如；Do you like tea with sugar ?此句的主语如果改为她就要把do改为does如下：Does she like tea with sugar ? did则是do,does的过去式表示发生在过去的行为或动作。例如：Did you have lunch ?...
do是原形，does是第三人称单数（he, she, it)形式；did是过去式：I/we/you/they dohomework in the morning.He/She/Xiao Ming does homework in ....We/THey/You/I/She/He did homework yesterday.do 还可以是...
