Brug af variabel i mysql query

Kan nogen forklare hvor dette virker:

$conn = mysql_connect($DBhost,$DBuser,$DBpass);
mysql_select_db("$DBName");


for ($i = 0; $i< 5; $i++) {
$qr = mysql_query("select * from photo WHERE category = 'Landscape' ORDER BY RAND() LIMIT 1");
$row = mysql_fetch_array($qr);
extract ($row);
make_random ($file, $category, $intro[$i]);
}

mysql_close($conn);


Mens dette IKKE virker:

$conn = mysql_connect($DBhost,$DBuser,$DBpass);
mysql_select_db("$DBName");
$choice = 'Landscape';

for ($i = 0; $i< 5; $i++) {
$qr = mysql_query("select * from photo WHERE category = $choice ORDER BY RAND() LIMIT 1");
$row = mysql_fetch_array($qr);
extract ($row);
make_random ($file, $category, $intro[$i]);
}

mysql_close($conn);

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