哪里错了？
<!DOCTYPE html>
<html>
<head>
<title> 事件</title>
<script type="text/javascript">
function count(){
var a=parseInt(document.getElementBId("txt1").value);
var b=parseInt(document.getElementBId("txt2").value);
var x=document.getElementBId("select").value;
var c=0;
switch (x){
case "+":
c=a+b;
break;
case "-":
c=a-b;
break;
case "*":
c=a*b;
break;
case "/":
c=a/b;
break;
}
document.getElementBId("fruit").value=c
}
</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()" /> <!--通过 = 按钮来调用创建的函数，得到结果-->
<input type='text' id='fruit' />
</body>
</html>
