Final answer:
The predicate of the sentence is the phrase "walk dangerously close to volcanoes to study them," which includes the verb and additional details about the action taking place.
Step-by-step explanation:
The predicate in the sentence "Scientists walk dangerously close to volcanoes to study them" is "walk dangerously close to volcanoes to study them." In English grammar, the predicate is the part of the sentence that tells us what the subject does or is. It includes the verb and all other details that describe what is going on. In this case, "walk" is the verb, and "dangerously close to volcanoes to study them" provides additional information about how and why the scientists walk.