gistfile1.cs

public class Order
{
  private Customer customer;
  private ISendEmail sendEmail;

  public Order(Customer customer, ISendEmail sendEmal)
  { 
    this.customer = customer;
    this.sendEmail = sendEmail;
  }

  // snip

  public void Place()
  {
    // place order

    sendEmail.ConfirmationTo(customer.EmailAddress);
  }
}