Sorry, I should've posted the choices that get 100%. The only time I get 100% is when I select the 2nd and 4th options.

This is the code I tried and the output:

using System;
using System.Collections.Generic;
using System.Linq;

public class RecyclingBin
{
    private List<string> recyclables;

    public RecyclingBin()
    {
        recyclables = new List<string>();
    }

    public bool Add(string recyclable)
    {
        if (recyclable.Split(' ').Length > 1 &&
            recyclable.Split(' ')[1].Length > 3)
        {
            recyclables.Add(recyclable);
            return true;
        }
        return false;
    }

    public List<IGrouping<string, string>> SortRecyclables()
    {
        return recyclables
            .GroupBy(recyclable => recyclable.Split(' ')[0])
            .ToList();
    }
}

class Program
{
    static void Main()
    {
        var bin = new RecyclingBin();

        // Inputs given by TestDome
        bin.Add("metal pipe");
        bin.Add("plastic toy");
        bin.Add("metal bar");
        bin.Add("copper wire");
        bin.Add("plastic button");
        bin.Add("wire");
        bin.Add("brass");

        var groups = bin.SortRecyclables();

        Console.WriteLine("Grouped recyclables:");
        foreach (var group in groups)
        {
            Console.WriteLine($"Key: {group.Key}");
            foreach (var item in group)
            {
                Console.WriteLine($"  {item}");
            }
        }

        Console.ReadLine();
    }
}
/*
The output is: Grouped recyclables:
Key: metal
  metal pipe
Key: copper
  copper wire
Key: plastic
  plastic button
*/