Which of the following prefixes indicates a position that is "surrounding"?

The prefix that indicates a position that is "surrounding" is indeed "peri-." This prefix is derived from Greek and translates to "around" or "surrounding" in English. It is commonly used in various medical and anatomical terms to denote something that encircles or encompasses a particular area or structure. For example, "pericardium" refers to the membrane surrounding the heart.

The prefix "para-" usually means "beside" or "near" rather than surrounding. "Intra-" means "within" or "inside," indicating something that is located internally rather than surrounding. "Ex-" typically means "out" or "outside," which also does not relate to the concept of surrounding. Therefore, "peri-" is the most accurate choice for indicating a surrounding position.