checked="true" 选中状态
checked="false" 未选中状态
checked属性不支持三元运算符
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>Insert title here</title>
</head>
<body>
<form>
<input onclick="alert(1)" type="radio" name="sex" value="male" >Male
<br>
<input type="radio" name="sex" value="female" checked="true">Female
</form>
</body>
</html>