Read the following context and choose the best option to answer the question.
Context: I just spent a solid whack of time in the mountains , six full days out of the last eight hiking in Garibaldi Provincial Park . And I could n't be happier still feeling the burn in my legs . It started last Sunday with a 30-plus kilometre day trip into the Diamond Head area .
Question: What is causing the narrator to be presently so exhausted ?
Options: 
A. None of the above choices .
B. They could n't get to bed .
C. They did not sleep the night before .
D. They just hiked a great distance .


D