using System;
using System.Text.RegularExpressions;
public class Example
{
    public static void Main()
    {
        string pattern = @"\.gif\?([^=]+=[^=]+&)+[^=]+(=[^=]+)?""";
        string substitution = @".gif""";
        string input = @"
<img src=""https://media.giphy.com/media/m7jzopL8Dm1kA/giphy.gif?cid=ecf05e4785d70ac4724a4083945ea6171d95688bf6a8a282&rid=giphy.gif&ct=g""  /> ";
        RegexOptions options = RegexOptions.Multiline;
        
        Regex regex = new Regex(pattern, options);
        string result = regex.Replace(input, substitution);
    }
}
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for C#, please visit: https://msdn.microsoft.com/en-us/library/system.text.regularexpressions.regex(v=vs.110).aspx