In ancient times, athletes, chosen by their city states, came to Olympia from every part of the Greek world. The bolded part is a participial phrase.
These refers to the group of words which contain a participle, modifiers etc and acts as adjectives.
The word 'chosen' is a participle which thereby makes it a participial phrase and is denoted as option B.
Read more about Participial phrase here https://brainly.com/question/8403140
#SPJ1