get single random record from given categories in mysql

i have a table in my sql mcq-quiz

id  question    category
1   q1  c1
2   q2  c1
3   q3  c1
4   q4  c2
5   q5  c2
6   q6  c3
7   q7  c3
8   q8  c4
9   q9  c4
10  q10 c5

i want single record from given category ... but record should be random..

i have tried the following query

 SELECT id, question, category  FROM `mcq_quiz` where category in(c1,c2,c3,c4,c5) group by category 

it is doing good job ... but retrieves same records every time but i want new and random record every time.. ( i have 2000 records in my original table)

i also have tried rand() function, it retrieves the same records every time but change the sequesnce, but i need random record everytime... plz help me to sortout this ... thanks in advanced