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<!DOCTYPE html>
<html>
<body>
<p>Display some text when the checkbox is checked:</p>
<label for="myCheck">Checkbox:</label> 
<input type="checkbox" id="myCheck" onclick="myFunction()">
<p id="text" style="display:none">Checkbox is CHECKED!</p>
<script>
function myFunction() {
  var checkBox = document.getElementById("myCheck");
  var text = document.getElementById("text");
  if (checkBox.checked == true){
    text.style.display = "block";
  } else {
     text.style.display = "none";
  }
}
</script>
</body>
</html>