Learn how to say a basic pronoun "this/that (thing)" in Korean and how it combines with the different particles.
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이 is this
그 is that (close to other person, far from you)
저 is that (far from both of you)
to say this and that, you have to combine those with the noun thing which can be 것(formal) or 거(casual).
이거 뭐예요 What is this?
그거/저거 뭐예요 What is that?
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Pay attention to the different contractions!