What is the singular version of criteria, and why is it irregular? a. criterion is the singular version, and it is irregular because it is a greek word in which the –on is changed to –a in its plural form. b. criteris is the singular version, and it is irregular because it is a greek word in which the –is is changed to –a in its plural form. c. criterium is the singular version, and it is irregular because it is a greek word in which the –um is changed to –a in its plural form. d. criterion is the singular version, and it is irregular because it is a latin word in which the –on is changed to –a in its plural form. select the best answer from the choices provided a b c d