Answer:
c. Ist.
Step-by-step explanation:
A suffix is a word that is added to the end of a word to make a new word, changing both the meaning and functions of that word.
Among the numerous suffix forms available, "-ist" indicates a person who studies a particular field, or follows a certain ideology or principle, or is an expert in a certain field. For example, a dermatologist is a word derived from the root word "dermatology" meaning the study of skin, and the suffix "-ist", making a new word that refers to the person practicing that profession.
Thus, the correct answer is option c.