求问小弟我自己写的这个DB类，错哪了，插不进数据

求问我自己写的这个DB类，哪里错了，插不进数据

<?php<br />
	class DB{<br />
		private $hostname;<br />
		private $username;<br />
		private $password;<br />
		private $select_db;<br />
		private $con;<br />
		private $Error;<br />
		<br />
		public function __construct($hostname,$username,$password,$select_db){<br />
			if(!empty($hostname)&&!empty($username)&&!empty($select_db))//检查参数是否为空，否则不赋值<br />
			{<br />
				$this->hostname = $hostname;<br />
				$this->username = $username;<br />
				$this->password = $password;<br />
				$this->select_db = $select_db;<br />
				$this->con = mysql_connect($this->hostname,$this->username,$this->password);<br />
				if(!$this->con){<br />
					$this->Error = die('Could Not Connect:'.mysql_error);<br />
				}<br />
				else{<br />
					mysql_select_db($this->select_db,$this->con);<br />
				}<br />
			}<br />
		}<br />
		public function __destruct(){//退出时结束连接<br />
			mysql_close($this->con);<br />
		}<br />
		public function insert($table,$body){//插入table中的一个数组<br />
			$line1 = implode(',',$body);<br />
			$line2 = implode(',',array_keys($body));<br />
			echo $sql = "INSERT INTO $table ($line2) VALUES ($line1)";<br />
			$result = mysql_query($sql,$this->con);<br />
			if(!$result){<br />
				echo $this->Error;<br />
				echo '111';<br />
			}<br />
			<br />
		}<br />
		public function update($table,$body){<br />
		<br />
		}<br />
		public function read($table,$keyword){<br />
			<br />
		}<br />
		public function delete($table,$keyword){<br />
		<br />
		}<br />
		public function getLastError(){//返回最后一条错误信息<br />
			return $this->Error;<br />
		}<br />
	}<br />
?>

<?php<br />
require('DB.class.php');<br />
	$DB = new DB('localhost','root','','dbtest');<br />
	$line1 = array(<br />
			'aa'=>'`aa`',<br />
			'bb'=>'`dd`'<br />
	);<br />
	$DB->insert('1234',$line1);<br />
?>