求问我自己写的这个DB类，哪里错了，插不进数据

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

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