Answer: D) Suffix.
Explanation: an affix is an addition to the base form or stem of a word in order to modify its meaning or create a new word. They can be at the beginning of the word (prefix) or at the end of the word (suffix). The particle "-less" that is at the end of the word "priceless" is an example of a suffix, added to the root word "price" so the correct answer is the corresponding to option D.