void page4() {
  String t = "Step 4 - The Test Statistics";
  textFont(myboldfont, 18);
  text(t, 30, 160);

  t = "Which test statistic formula should be used in this case? Choose the appropriate one then click Answer:";
  drawStrings(t, 30, 200, 25);

  if (cb4.selectedIndex()==0) {
    image(test1, 300, 230);
  }
  else if (cb4.selectedIndex()==1) {
    image(test2, 300, 230);
  }
  else {
    image(test3, 300, 230);
  }

  fill(0, 0, 255);
  drawStrings(feedback, 80, 360, 25);

  tf3.setVisible(false);
  cb4.setVisible(true);
}