Sub-Query doens't work

Sub-Query doens't work

Table "Questoes";
+----------+--------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+----------+--------------+------+-----+---------+----------------+
| id | int(11) | NO | PRI | NULL | auto_increment |
| id_quest | int(11) | NO | | NULL | |
| questao | varchar(255) | NO | | NULL | |
| nivel | int(11) | NO | | NULL | |
| tipo | varchar(255) | NO | | NULL | |
+----------+--------------+------+-----+---------+----------------+
Table "Respostas";
+----------+---------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+----------+---------------+------+-----+---------+----------------+
| id | int(11) | NO | PRI | NULL | auto_increment |
| id_quest | int(11) | NO | | NULL | |
| resposta | varchar(255) | NO | | NULL | |
| r_valido | enum('0','1') | NO | | NULL | |
+----------+---------------+------+-----+---------+----------------+
My query is:
SELECT q.questao, r.resposta
FROM questoes q, respostas r
WHERE q.id_quest IN (19,20,21)
AND q.id_quest=r.id_quest
AND r.r_valido = ( SELECT resposta FROM respostas WHERE r_valido= 1 )
What I need is the field questao from table Questoes and the field
resposta from table respostas where field r_valido = 1. The field resposta
have 4 results, and only one is valid, in other words, where the field
r_valido = 1.