Final answer:
The phrase in question contains a participle, which is 'driven' modifying the noun 'swimmer'. The correct answer is option b.
Step-by-step explanation:
The phrase 'driven by the need to be the best in the world' contains a participle, which is a verb form used as an adjective to modify a noun or pronoun. In this case, 'driven' is the past participle of the verb 'drive', modifying the noun 'swimmer' and expressing the cause of his anxiety. Therefore, the correct answer to the question is option b. participle.