JavaScript - Crear Cuestionario en Java script

<select id="select1">

<option value="00">Pregunta 1</option>

<option value="60">A</option>

<option value="40">B</option>

<option value="20">C</option>

<option value="10">D</option>

</select>

<select id="select2">

<option value="00">Pregunta 2</option>

<option value="60">A</option>

<option value="40">B</option>

<option value="20">C</option>

<option value="10">D</option>

</select>

<select id="select3">

<option value="00">Pregunta 3</option>

<option value="60">A</option>

<option value="40">B</option>

<option value="20">C</option>

<option value="10">D</option>

</select>

<select id="select4">

<option value="00">Pregunta 4</option>

<option value="60">A</option>

<option value="40">B</option>

<option value="20">C</option>

<option value="10">D</option>

</select>

<button type="button" onclick="test()">Suma</button>

<h2 id="result"></h2>

<script>

function test() {

var a =+ document.getElementById("select1").value;

var b =+ document.getElementById("select2").value;

var c =+ document.getElementById("select3").value;

var d =+ document.getElementById("select4").value;

document.getElementById("result").innerHTML = a + b + c + d;

}

</script>