there are only three keys to staying young and happy为什么用staying There are secrets to staying y...

\u5206\u6790\u53e5\u5b50There are only four secrets to staying young, being happy, and achieving success.

to\u8fd9\u91cc\u662f\u505a\u4ecb\u8bcd\u7528\uff0c\u4ecb\u8bcd\u77ed\u8bed\u505a\u5b9a\u8bed\u4fee\u9970\u524d\u9762\u7684secrets

\u201dthere be...\u201d\u53e5\u578b\u662f\u5b58\u5728\u53e5\u7684\u5e38\u7528\u57fa\u672c\u7ed3\u6784\uff0cthere\u5728\u53e5\u4e2d\u5904\u4e8e\u4e3b\u8bed\u4f4d\u7f6e\uff0c\u8d77\u5f62\u5f0f\u4e3b\u8bed\u7684\u4f5c\u7528\uff0c\u771f\u6b63\u7684\u4e3b\u8bed\u662f\u968f\u540e\u7684\u540d\u8bcd\u8bcd\u7ec4\u3002

首先我不认为to 是介词，to 就是一个表目的状语的词，如果非要说问题，我认为问题是错的，相信你本能的直觉，别把自己弄混了，如果你还有点半信半疑，大不了开学可以问老师啊，先让问题保留，你觉得呢？

staying此处是保持的意思。
只有三个要素可以让你保持年轻与快乐。

to 在是介词，后面应接动词ing形式。
此动名词结构位于介词to的后面，做宾语
保持年轻快乐只有3个秘诀。

to是介词吧，介词后加doing

to 在这里是介词，后面是动词ing形式。
有不懂的欢迎追问

扩展阅读：children of the dark ... there is only some old ... i in this room watching ... the bottom of the ocean ... this is mary ... children s day ... there is no reason why ... there is only thing that ... there is one and only ...