Read the following context and choose the best option to answer the question.
Context: After a long flight we sure love to get a good sleep . But it 's afternoon in Beijing and we need to adjust to the local time . We took a quick nap and woke up in the early evening in time to take a stroll around the neighborhood . Our hostel is nearby the old drum tower which is located near a busy street .
Question: Why does a long flight require the speaker to then have to adjust to the local time ?
Options: 
- None of the above choices .
 - Because they were the one flying the plane and therefore could not sleep
 - Because the flight was too noisy to sleep on and they are exhausted
 - Once you 've entered a new region , your body must acclimate to the time difference


Once you 've entered a new region , your body must acclimate to the time difference