Hello Nidhi!

You can go for any course for your graduation. The elgibility for the entrance exam to fill the posts of CBI officers is 50% marks in your graduation and your age must not exceed 25 years. After your graduation, you have to appear combined graduate examination conducted by UPSC(conducted once in a year). After this you would be called for a medical examination and personal interview. If you successfully get through these formalities , you will become a CBI officer.

CBI also recruits candidates through direct recruitment, deployment, promotion of seniority, or limited review of departmental competence. This recruitement is done by SSC.

Hope you are clear!

Greetings!
To become a Group-A officer in CBI, you have to become an IPS officer by passing the Civil Services Examination conducted by UPSC. To become a sub-inspector in CBI, you have to take SSC CGL exam. In CBI Sub Inspector Test (SSC CGL), Tier 1 and Tier 2 examinations are of objective type.

I hope this was helpful. Thank you!