Given a scientific question, generate a correct answer to it.

Input: Consider Input: The nitrogen that enters living systems by nitrogen fixation is successively converted from organic nitrogen back into nitrogen gas by what?

Output: bacteria

Input: Consider Input: What are the two most common vision problems?

Output: nearsightedness and farsightedness

Input: Consider Input: In mismatch repair, other enzymes remove and replace incorrectly paired nucleotides that have resulted from what?
Output: replication errors