Sentence provides commentary information for elaboration of a concrete detail.
D) It was a good idea to wear short sleeves and a light jacket that could be taken off easily in the afternoon.
The concrete detail:
short sleeves and a light jacket
The commentary information for elaboration of the concrete detail:
that could be taken off easily in the afternoon.
D. Audience members who stood in front of the stage to watch plays.
Identifying the setting, main character, and plot, taking special note of rising action, climax, and denouement. Hope this helps have a nice day.
The t-shirt that they give only to people who finish is a big reason that so many people take up the challenging race.
This paraphrase presents the same information as in the sentence, but since it should be a bit more of a summary, it takes out the specific detail of how many people actually run the race, which can just be paraphrased into 'so many'.