Supposed I had the following `HTML` form:

```
<html xmlns="http://www.w3.org/1999/xhtml">
<head><meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
  <title>Choose</title>
</head>

<body>
  <form method="post" enctype="application/x-www-form-urlencoded">
    <h1>Choose</h1>

    <p><input type="radio" name="choose" value="psychology"><font size="5" color="#0033CC">Instant Psychology</font><br>
    <br>
    <input type="radio" name="choose" value="geography"><font size="5" color="#CC0000">Instant Geography</font><br>
    <br>
    <input type="radio" name="choose" value="gastronomy"><font size="5" color="#660033">Instant Gastronomy</font><br>
    <br>
    <input type="submit" name="Submit" value="Go"></p>
  </form>

</body><link rel="stylesheet" type="text/css" href="data:text/css,"></html>

```

How can I write a `JavaScript` function to make sure at least one radio input has been selected?