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                        /初識HTML(5)+CSS(3)-升級版

單選選中后怎么取消選中

<html>
<head>
<title>用戶信息注冊</title>
<style>
.Item{
font-size:8px;
}
</style>
</head>
<body?align="center"?>
<h2?>用戶注冊表單</h2>
<form?method="post"?>
<p>用&nbsp;戶&nbsp;名&nbsp;:<input?type="text"?name="user"?size="12"?maxlength="20"?required="required"?placeholder="不超過20個字">
</p>
<p>昵&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;稱&nbsp;:<input?type="text"?name="username"?size="12"?maxlength="20"?required="required"?placeholder="不超過10個字">
</p>
<p>登陸密碼:<input?type="password"?name="password"?size="12"?minlength="8"?required="required"?placeholder="至少為8位">
</p>
<p>性別:
<input?type="radio"?name="sex"/>男
<input?type="radio"?name="sex"/>?女</p>
<p>?聯系電話:
<input?type="tel"?name="tel"?required="Required"></p>
<p>電子郵件:<input?type="text"?name="email"?required="required"></p>
<p>聯系地址:<input?type="text"?name="address"?required="required"></p>
<p?class="Item"><input?type="radio"?name="item"?required="requied"?style="width:8px;height:8px;">同意注冊項目服務條款</p>
<input?type="submit"?value="注冊">&nbsp;
<input?type="reset"?value="清除">
</form>
</body>
</html>