using System;
using System.Text.RegularExpressions;
 
public class Test
{
	public static void Main()
	{
		string pattern = @"(?<=\d)\s+(?=(?:\d+\s+)*\d+\s+(?:eur|usd)\b)";
        string substitution = @"";
        string input = @"sdklfjsd 10   343 usd ds 232 300 eur
 
sdklfjsd 10   343 usd ds 232 300 eur    test
2 300 $ 12 Asdsfd 2  300  530 usd and 2  351 eur";
        RegexOptions options = RegexOptions.Multiline;
 
        Regex regex = new Regex(pattern, options);
        string result = regex.Replace(input, substitution);
        Console.WriteLine(result);
	}
}

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