Which answer is a continuation of the following symbolic pattern?

The answer is SSSSSSSSSSSS. If you look at it, its going by alphebetical order. "P,Q,R" So next comes "S." Then you will notice that it increases by 3. There was 3 "P". There was 6 "Q". Then there was 9 "R". Then the next should be 12. So 12 "S".