Question

jaden flew back to switzerland during winter break. for a couple days, he had trouble falling asleep at night even though he felt tired all day. these is most likely because there was a change in his \
a pineal gland
b sleep hygiene
c sympathetic nervous system
d circadian rhythm

Explanation:

Circadian rhythm refers to the internal 24 - hour biological clock that regulates sleep - wake cycles. When a person travels across time zones (as Jaden did when flying back to Switzerland), it disrupts the circadian rhythm, leading to symptoms like daytime tiredness and difficulty falling asleep at night (jet lag). The pineal gland (A) is involved in producing melatonin (related to sleep), but the key concept here is the disruption of the overall circadian pattern. Sympathetic Nervous System (C) is part of the autonomic nervous system (arousal, "fight - or - flight"), not directly related to jet - lag - type sleep issues. Sleep hygiene (B) refers to practices that promote good sleep (e.g., regular bedtime, no screens before bed), which is not the issue here as the problem is due to travel across time zones (circadian rhythm disruption).

Answer:

D. Circadian rhythm