AdaptiveCard

Activity activity = new Activity()
{
    Attachments = new List<Attachment>()
    {
        new Attachment()
        {
            ContentType = AdaptiveCard.ContentType,
            Content = new AdaptiveCard("1.0")
            {
                Body = new List<AdaptiveElement>()
                {
                    new AdaptiveTextBlock()
                    {
                        Text = $"Lorem reminder",
                        Size = AdaptiveTextSize.Large
                    },
                    new AdaptiveTextBlock()
                    {
                        Text = $"$"Hi {userName},\r\nYou've missed some lorem ipsum dolor sit amet:\r\n- **consectetur:** Ut porttitor\r\nChoose an action from below to add them.""
                    }
                },
                Actions = new List<AdaptiveAction>()
                {
                    CreateCardAction("First action"),
                    CreateCardAction("Second action")
                }
            }
        }
    },
    From = turnContext.Activity.Recipient,
    Recipient = turnContext.Activity.From,
    Type = "message",
    Conversation = turnContext.Activity.Conversation
};