Answer:
D-past
Step-by-step explanation:
Everyone in the climbing expedition \"developed\" frostbite from their exposure to the cold . The main verb is in the past since the time reference climbing expedition signals that the action took place when this expedition took place. Everyone who had taken part of that expedition developed frostbite as a consequence of being exposed to the cold weather. So, those people got some health problems in the past , which is a definite situation we can talk about in the present.