Answer:
The answer is option C.
Step-by-step explanation:
An INTRODUCTORY PHRASE does not have subject and verb, it only sets the stage for the main clause.
Sentences A and D begin with their subjects 'Natan' and 'Every member of the team' respectively while sentence B begins with an adverb.
Sentence C is the only one with an introductory phrase "after the 20-mile hike' that refers to when the action took place.