i m going to take electrical branch, want 2 prepare upsc exam online throught out collage days. plz suggest me best coaching, 2 optional sub

i want class-a post. while during the preparation of upsc , could i get into drdo. for ee branch , which 2nd optional subject is better for upsc. please tell me all about all post of class-a and class-b through ee branch. what qualification is required to get into drdo