one day when they are having dinner我猜这个带when可能表示进行时所以用having,但下一句i am very busy,when people go out to dinners这里也是when开头为什么没用ing的进行时呢,还有我知道有时候dinners与a dinner意思一样,如go out to dinners和shall we go out to a dinner tonight?所以我认为one day when they are having dinners对吗?如go out to dinners和shall we go out to a dinner tonight？所以我认为one day when they are having dinners对吗？dinner加s对吗请求大家帮助！

是正确的，此句强调正在进行i am very busy when people go out to dinners此句只强调人们去吃晚饭这个短暂动作，不用进行时希望我的回答对你有所帮助

when people go out to dinners,指的是“当人们去吃饭的时候”,泛指人们想去吃饭的那一段时间或者是过程,不是具体某一群人或者某一个时间.比如,当人们去吃饭的时候都要考虑他们有多少时间.When people go out to dinners,they always consider how much time they have.这是描述一个事情或者事实.
one day when they are having dinner,指的是“那天他们吃饭的时候”,指的是明确的在那一天,那一些人吃饭的那个时间,所以用进行时,因为在那个时间点那些人就是正在进行吃饭这个动作.