It keeps on "Bummer! Is FitnessRecord._entries of type System.Collections.Generic.List<Treehouse.CodeChallenges.Activit"

using System.Collections.Generic;
using System.Collections.ObjectModel;
//using System.Collections.Generic.IEnumerable;



namespace Treehouse.CodeChallenges
{
    public class FitnessRecord
    {
        public static List<ActivityEntry> entries1 = new List<ActivityEntry>();

        private ReadOnlyCollection<ActivityEntry> _entries = new ReadOnlyCollection<ActivityEntry>(entries1);

        public IEnumerable<ActivityEntry> Entries { get { return _entries; } }
    }
}

using System;

namespace Treehouse.CodeChallenges
{
    public class ActivityEntry
    {
        public string Name { get; set; }
        public DateTime Started { get; set; }
        public DateTime Finished { get; set; }
    }
}