using System;
using System.Linq;
using System.Collections.Generic;
public class Test
{
public static void Main()
{
string instr = "test";
int startIndex = 1;
int length = 2;
char[] chars = instr
.Where((c, i) => i >= startIndex && i < startIndex + length).ToArray();
Console.Write(new string(chars));
}
}
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