ASP.NET: Dependency Injection

// Object A - the class that depends on Object B
class Reviewer 
{
  private EmailSender Sender = new EmailSender();  
  public SendReview(string lesson, string comments)
  {
    Sender.SendReview(lesson, comments);
  }
}

// Object B - the dependency
class EmailSender
{
  public SendReview(string lesson, string comments)
  {
    // Send an email with the Lesson and Comments
  }  
}

static void Main(string[] args)
{
  Reviewer reviewer = new Reviewer().
    SendReview("Dependecy Injection", "Learned a ton!");
}