Aoa, sir can you please tell us that how you select your optional subjects mean on what basis you select it?

Few factors might assist you to select your optional options.
Firstly, select all subjects about which you are familiar or makes you comfortable.
Secondly, check stats of previous CSS exams about subjects which are scoring subjects.
Thirdly, analyze that which subject is going to be selected by maximum number of candidates, skip those subjects. Because if you check stats accurately, you will know that a subject gets hit (maximum failure rate) in which too much candidates try to attempt it. Then it becomes difficult for FPSC to pass much of students in that subject.
Fourthly, after checking the stats, check that which subject got hit in recent years and which subject is going to get hit, so you should skip that subject too.
Fifthly, don't go for the subjects which have lengthy syllabus or have low scoring trend.
Lastly, check syllabus and past papers of subjects, this will let you to decide, in which direction you should go.

What could be the alternate subjects to Environmental Sciences that are short and concrete? I have aptitude in science subjects, but many seniors discourage the idea of opting them in CSS, which dithers me now.