Which suffix indicates a person who specializes in a field?

The suffix that indicates a person who specializes in a particular field is "-ician." This suffix comes from Latin, often denoting a profession or a person skilled in a specific area of study or practice. For example, a "physician" is a medical doctor, highlighting expertise in the field of medicine, while a "musician" specializes in music.

The other suffixes do not convey this specific meaning. "-ism" generally refers to a doctrine, system, or practice, such as in "activism" or "Buddhism." "-ion" typically denotes an action or condition, as seen in words like "action" or "reaction." Lastly, "-ile" refers to capability or tendency, as in "ductile" or "fertile," rather than denoting a specialized person. Thus, "-ician" is the correct choice for indicating someone proficient in a particular domain.