input radio 怎么提交数据啊？

<form action="" method="get">
<input type="radio" name=a value="ccc">
<input type="radio" name=a>
<input type="radio" name=a>
<input type="radio" name=a>
<input type="radio" name=a>
<input type="radio" name=a>
<input type="radio" name=a>
<input type="radio" name=a>
<input type="submit" />
</form>为什么提交的地址是?a=on
怎么才能提交为?a=ccc