why the sort result is different with C#

[Luis via Digitalmars-d-learn]

On Friday, 22 January 2016 at 06:53:29 UTC, mzfhhhh wrote:
> D code:
> auto arr = ["b1=1", "b=2","a1=1", "a=2"];
> writeln(arr.sort());
>
> output:["a1=1", "a=2", "b1=1", "b=2"]
>
> C# code:
> var arr = new string[]{ "b1=1", "b=2", "a1=1", "a=2" };
> Array.Sort(arr);
>
> output:["a=2","a1=1","b=2","b1=1"]

I don't what string sorting criteria is using C#, but '9' < '=', 
so should be ["a1=1", "a=2", "b1=1", "b=2"]