Why the BlenaEthch only can be installed Windows's C:\?

My computer is Dell Inspiron 531s.
OS is windows10(ver Chinese).
My computer‘s C:\ disk has not insufficient space。
I was ready to install the balenaEtcher into D:.
I was suprised thar the balenaEtcher has not the choice.The balenaEtcher automaticly installed the C:. Can you help me?