11.21 Write a program that plays the game of concentration. Use a series of PictureBox controls to display the images. When the user Clicks on a PictureBox, the image associated with that PictureBox is displayed. Clicking a second PictureBox displays the image associated with the second PictureBox. If the images match, they remain displayed. If they do not match, both images should be hidden.
(Question taken from: "Visual Basic 6: How to Program" by Deitel & Deitel T. R. Nieto)