random specific entry from database

[Ramtree]

i need to random an entry where question_answered = $_POST['randompick'] (the form).

$r_pick = $_POST['randompick'];

$randomvar = "mysql_query(SELECT * FROM quiz_correct_response WHERE question_answered = $r_pick ORDER BY rand() LIMIT 1)";
  while($pick = mysql_fetch_array($randomvar))
  {
  echo $pick[0];
  }

 

but somehow it's giving me error

Warning: mysql_fetch_array(): supplied argument is not a valid MySQL result resource

 

please help me if you can, thanks

[ignace]

$randomvar = "mysql_query(SELECT * FROM quiz_correct_response WHERE question_answered = $r_pick ORDER BY rand() LIMIT 1)";

 

should be:

$randomvar = mysql_query("SELECT * FROM quiz_correct_response WHERE question_answered = $r_pick ORDER BY rand() LIMIT 1");