Answer:
B). Appositive phrase
Step-by-step explanation:
The bold words in the given sentence('a contemporary of Ralph Waldo Emerson') exemplify an appositive phrase as it functions to define the noun 'Oliver Wendell Holmes' which it follows. The appositive phrases primarily function to identify, define, or rename the noun or noun phrase it succeeds. The use of commas suggests that the appositive phrase provides further/bonus information to identify the noun. Thus, option B is the correct answer.