C#

private void printPreviewToolStripMenuItem_Click(object sender, EventArgs e)
        {
printPreviewDialog1.Document = this.printDocument1 ; // Attach PrintDocument to PrintPreview Dialog
            printPreviewDialog1.FormBorderStyle = FormBorderStyle.Fixed3D ;
            printPreviewDialog1.SetBounds(20, 20, this.Width, this.Height);

 if (printPreviewDialog1.ShowDialog()== DialogResult.OK)
            {
                 this.printDocument1.Print();
                
            }

private void backgroundWorker1_DoWork(object sender, DoWorkEventArgs e) 
{ 
Assessment.Update() 
} 

foreach (Cat thisCat in zooAnimals.OfType<Cat>())
{
   thisCat.pet();
}

foreach (Dog thisDog in zooAnimals.OfType&lt;Dog&gt;())
{
   thisDog.pet();
}

foreach (Cat thisCat in zooAnimals.OfType<Cat>() || Dog thisDog in zooAnimals.OfType<Dog>())
{
    thisCat.pet();
    thisDog.pet();            
}