问如何访问单选按钮的值

EN

function check() {
var a = document.getElementById("test").value
if (a === "one") {
alert("Correct!")
} else {
alert("Wrong!")
}
}

<h1><center>Simple Quiz</center></h1>
<br>
1) What is 1 + 1?
<br>
<form>
  <input type="radio" name="one" id="test" value="one">1<br>
  <input type="radio" name="one" id="test" value="two">2<br>
  <input type="radio" name="one" id="test" value="three">3<br>
  <button onclick="check()">Check</button>
</form>