-도 means ‘also’ or ‘too’. It is not an adverb, it is a particle which is attached to a noun(no space between noun and -도). And -도 cannot be with Topic particle(-은/는), Subject particle(-이/가) and Object particle(-을/를), which -도 substitute those particles. For example,
A: 저는 한국 사람이에요. (I am Korean.)
B: 저도 한국 사람이에요. (I am also Korean.)
C: 저도요! (Me too!)
A : 저는 사과를 좋아해요. 배도 좋아해요. (I like apples. I also like pears.)
A: 저는 사과를 좋아해요. 동생도 사과를 좋아해요. (I like apples. My sister/brother also likes apples)
A: 저는 기타를 쳐요. 그리고 피아노도 쳐요. (I play guitar. And I also play piano.)
*A lot of my students get confused by -도 and 또 because they have similar pronunciation and meaning. But they are different.
-도 is a particle while 또 is an adverb which -도 is attached to a noun but 또 is used independently. And -도 means ‘also’ or ‘too’, 또 means ‘again’, ‘and’ or ‘in addition’. For example,
저도 사과를 먹었어요. (I also ate an apple. -> no space between 저and 도)
저 또 사과를 먹었어요. (I ate an apple again. -> a space between 저 and 또)
민수는 한국 사람이에요. 수지도 한국 사람이에요. (Minsu is Korean. Suji is also Korean.)
민수는 자전거를 탈 수 있어요. 또 운전도 할 수 있어요. (Minsu can ride a bike. And he can also drive a car.)
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