Q: 133 (IAS/1997)

In the series POQ, SRT, VUW, ? The blank space refers to
question_subject: 
Logic/Reasoning
question_year: 
1997
question_exam: 
IAS
question_sub_subject: 
Reasoning
question_topic: 
Analytical
stats: 
0,304,56,24,16,304,16