The word "typo" in line 25 is discussing an error in the transcription process from DNA to RNA. In my opinion, outside scientific knowledge of transcription really helps for this question, but even without it we can make do using context. The process of going from DNA to RNA is described in the passage as "transcribed" which implies to write out. A "typo" in writing something out would be miscopying or mistakenly writing. This is answer choice C.
Answer choices A and B are simply distraction answer choices that if we can figure out the general idea of what transcription is, should be fairly easy to dismiss.
Let me know if this was helpful, and please ask if you have any other questions.