sql server 读取时出错

SqlConnection myCon = new SqlConnection();
        myCon.ConnectionString = "Persist Security Info=False;User id=sa;pwd='';database=nettest;server=(local)";
        myCon.Open();
        Page.Response.Write(myCon.State + " <br/>");   
        SqlCommand myCom=new SqlCommand();
        myCom.Connection =myCon;
        myCom.CommandText="select * from t_pass";
        SqlDataAdapter sdr = myCom.ExecuteReader();

最后一句：SqlDataAdapter sdr = myCom.ExecuteReader();报错：
编译器错误信息: CS0029: 无法将类型“System.Data.SqlClient.SqlDataReader”隐式转换为“System.Data.SqlClient.SqlDataAdapter”

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怎么才能修正错误呢。

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System.Data.SqlClient.SqlDataReader sdr = myCom.ExecuteReader();
或者
SqlConnection scon = new SqlConnection(ConfigurationManager.AppSettings["ConnectionString"]);
        scon.Open();
        SqlDataAdapter dbAdapter = new SqlDataAdapter(str, scon);
        DataSet ds = new DataSet();
        dbAdapter.Fill(ds);
        scon.Close();
这些写

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SqlDataReader sdr = myCom.ExecuteReader();

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using(SqlDataRead