답장 vs. 대답 vs. 답변
답장 - answer/reply
대답 - reply, answer, respond
답변 - reply (answer, respond)
답장 is more for written things. Like a letter or email.
...나에게 답장하는 것을 잊지 마라 (Don't forget to write back to me)
대답 - an answer, but when there is a definite answer or choice, or an expectation. More like a fact.
...묻는 말에 바른대로 대답하세요 (Please answer truthfully)
답장 - an answer, but with different choices or right answers, or an unknown expectation or a surprise. More like your opinion.
...아는 대로 답변해 주세요 (Please answer to the best of your ability)
Is this right? Please make any corrections or give your own explanation.
The sentences came from 네이버, by the way.