.Inside the gallery is a small bookstore___you can buy prints,boos and postcards.

답은 where인데

which는 안되나요?? 설명좀 부탁드려요

여기선 

this is a booksotre at which you can buy foreign magaines.

이유가 뭐죠 아래 문장에서는 which가 사용됬는데;;