the key to 后面接ing 还是do

the key to doing sth

做什么什么的关键，是介词，to词性不会发生变化的，只有用法上的区别

key to sth. 后面直接接名词. 动名词ing形式可用.

Exercise is the key to good health.
Exercise is the key to keeping health.

这里to是介词.

应该是the key to do sth,to后面的动词是不带ing的.

显然是the key to do sth.
一般而言，前面有to时，后面都要跟do sth.组成动词不定式
这儿句式和the answer to the question 大致相同

the key to sth./the key to doing sth.