public class TwitterMessagesProvider
{
public IEnumerable<string> GetMessages(string email)
        {
            // fetched from twitter
            return new[] { "Tweet1", "Tweet2" };
        }
}

public class FacebookMessagesProvider
{
        public IEnumerable<string> GetMessages(string email)
        {
            // fetched from facebook
            return new[] { "Message1", "Message2" };
        }
}

public class MessageListControl
{
    private readonly IMessageRenderer _messageRenderer;
    private readonly TwitterMessagesProvider _twitterMessagesProvider;
        private readonly FacebookMessagesProvider _facebookMessagesProvider;

        public MessageListControl(
        IMessageRenderer messageRenderer,
TwitterMessagesProvider _twitterMessagesProvider,
FacebookMessagesProvider _facebookMessagesProvider)
        {
        _messageRenderer = messageRenderer;
_twitterMessagesProvider = twitterMessagesProvider;
            _facebookMessagesProvider = facebookMessagesProvider;
        }

        public void RenderMessages(string email)
        {
        var tMessages = _twitterMessagesProvider.GetMessages(email);
            var fMessages = _facebookMessagesProvider.GetMessages(email);
            var messages = tMessages.Concat(fMessages).ToList();

           _messageRenderer.Render(messages);
        }
}