Answer:
a. positive
Explanation:
To determine the connotation of a word, it is important to look at the context in which it is used. The connotation of a word may be different from its literal meaning depending on the way it is used, the context in which it's placed, it's cultural associations, etc.
The word "triumphant" here has a positive connotation as it is mentioned in the context of satisfaction over one's hard work and achieving one's goal, a sense of victory in other words. It is followed by "athlete smiled brightly" on crossing the finish line of the race, which strongly suggests a positive connotation. This claim is further proved in the latter half of the statement which negates the possibility of any negative connotation by giving the reason for the athlete being triumphant.
