请问我错在哪里？
<!DOCTYPE html>
<html>
<head>
<title> 事件</title>
<script type="text/javascript">
function count(){
var a=document.getElementById(“txt1”）.value;
//获取第一个输入框的值
var b=document.getElementById(“txt2”）.value;
//获取第二个输入框的值
var c=document.getElementById(“select”）.value;
//获取选择框的值
var result=document.getElementById(“fruit”）.value;
switch(select){
case "+":
result=parseInt(a)+parseInt(b);
break;
case "-":
result=parseInt(a)-parseInt(b);
break;
case "*":
result=parseInt(a)*parseInt(b);
break;
case "/":
result=parseInt(a)/parseInt(b);
break;
}
//获取通过下拉框来选择的值来改变加减乘除的运算法则
document.getElementById(“fruit”）.value = result
//设置结果输入框的值
}
</script>
</head>
<body>
<input type='text' id='txt1' />
<select id='select'>
<option value='+'>+</option>
<option value="-">-</option>
<option value="*">*</option>
<option value="/">/</option>
</select>
<input type='text' id='txt2' />
<input type='button' value=' = ' onclick="count()"/>
<input type='text' id='fruit' />
</body>
</html>
