Thank you, I realy didnt)

Can anyone tell me why do I have exception: "src/Solution.cs(7,13): error CS0103: The name 'Array' does not exist in the current context", as I may suppose I cant use Array.Sort(a), but why? C#

There is defently something wrong with this Kata, my code works properly in IDE Visual Studio and passes all the Basic Tests, but it didnt work well here.

I thought, that Basic Tesrs are the same, do they?
Where can I see inputs without loosing honor?

As I may suppose, there is a mistake in this Kata when I try to resolve it on C#, because my code successfully completes Basic Tests when I "RUN SAMPLE TESTS", but error occur in Basic Tests when I try to "ATTEMPT"