Which of the following is an example of a prefix?

The choice "ante-" is correct because it is indeed a prefix used in medical terminology. Prefixes are word parts that are added to the beginning of a root word or combining form to modify its meaning. In this case, "ante-" means "before" or "in front of," which can be used in terms such as "antepartum" (before childbirth) or "anteflexion" (a condition in which an organ is bent forward).

The other options do not qualify as prefixes. "-algia," for instance, is a suffix that denotes pain, such as in "neuralgia." "Cardi/o" is a combining form related to the heart, often used in compound words like "cardiology." Lastly, "ECG" stands for electrocardiogram, which is an abbreviation and not a prefix or a word part used to modify other medical terms. Therefore, "ante-" is the only correct choice that exemplifies a prefix.