[A] alert = "Hello World"
[B] alertBox("Hello World")
[C] alert("Hello World")
[D] window.alert("Hello World")

The correct answer is C) alert("Hello World"). 

<script>
  alert("Hello World")
</script>

This code will display a pop-up window with the message "Hello World". It is a useful way to notify the user of important information, such as an error message or a warning.