The correct answer is C. Omission.
The word "omission" means the act of leaving something out. It is derived from the Latin word "omittere", which means "to let go" or "to leave out". The word "omission" is spelled with two "m"s and one "s".
The other options are incorrect because they are not spelled correctly. The word "ommission" is spelled with two "m"s and one "s", not one "m" and two "s"s. The word "omision" is also spelled with one "i", not two "i"s. The word "ommision" is spelled with three "m"s, not two "m"s.
I hope this explanation is helpful. Please let me know if you have any other questions.
