एपीए उद्धरण

Ashok Singh. (2019). UPSC Civil services prelims: General studies-1. wiley.

शिकागो स्टाइल उद्धरण

Ashok Singh. UPSC Civil Services Prelims: General Studies-1. New Delhi: wiley, 2019.

एमएलए उद्धरण

Ashok Singh. UPSC Civil Services Prelims: General Studies-1. wiley, 2019.