@asma mehvish
Yup! I would also suggest you to opt Public Ad. There are a couple of solid reasons for opting it: first, Public Ad's syllabus is almost the same as it was before regrouping, and you can consult just one or two recommended books for better preparation with somewhat certainty; second, it is not much difficult one or much technical one like some other subjects, and you can get even some ready-made topics from consulting English Newspapers esp. those columns that are written on ecology of bureaucracy, public dealings, etc. Another edge is that you can even consult some past papers for this subject as this is not a new or nascent subject in the arena of CSS.

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"But screw your courage to the sticking place,
And we'll not fail." _Shakespeare, 'Macbeth')