당연하지! 물론이지! 물론! 그치그치(그치, is expression of agreement. when U repeat it twice.., strengthening the original meaning. It is very colloquial expression, i usually use it. but you cannot use this to your senior. (coll,) 물론입니다. 그럼요. 그렇고 말구요(polite form) I recommend to use "당연하지" "그치그치" 당연히 is adv. or adj. 숙취때문에, 걔는 당연히 (수업에)안왔지. Of course he didn't attend the class, due to hangover.

당연히