这天他们很开心英语怎么说

“他们很开心”可以用英文表达为："They are happy." 或者 "They are feeling happy."
这个表达的来源来自于英语的基本语法，主语是"they"，谓语是"are"，表示"他们"的感受状态是"开心"。
下面是一些英文例句和中文翻译：
I can see that they are happy. 我看得出他们很开心。
They are feeling happy today. 他们今天很开心。
Their smiles show that they are happy. 他们的笑容表明他们很开心。
They are happy because they got what they wanted. 他们很开心，因为他们得到了想要的东西。