instruction:
Given a question and a context passage, generate the answer having the word or phrase from the context passage. Here, the answer should be a shortest continous span from the passage.
question:
Context: Amazonis Planitia is one of the smoothest plains on Mars. 
 Question: On what celestial body is Amazonis Planitia located?
answer:
mars


question:
Context: The 10th Cavalry returned from the Philippines in late 1902 and settled down in different posts in the south western United States. Patrols and garrison life was the routine for the regiment. Under war plans, the 10th was designated for service in the Pacific and support in the Philippines from 1915 through 1942 but never rotated there. The 9th Cavalry Regiment became "Park Rangers" in 1905 for Yosemite National Park and other state and federal lands. The Troopers' Campaign Hat, sporting the "Montana Pinch" used to help shed the tropical downpours. That "Montana Pinch" gave the hat the distinctive look we recognize today as the "Smokey Bear Hat". 
 Question: Which cavalry is credited with the Smokey Bear Hat, 10th or 9th?
answer:
9th cavalry regiment


question:
Context: Diurnal effects on motor control are evident in the human disease of Restless Leg Syndrome (RLS), which is purported to be linked to brain iron deficiency as well as alterations in dopaminergic systems. Thus, we explored the relationship between daily rhythms, the onset of motor dysregulation and brain iron deficiency in an animal model of iron deficiency. Male and female weanling Sprague-Dawley rats consuming control (CN) or iron-deficient (ID) diets were examined weekly for acoustic startle response (ASR) and prepulse inhibition (PPI) for a 5-week period. Iron deficiency reduced the magnitude, but not timing, of the ASR at specific time points. ASR was elevated 60% at the onset of the dark cycle relative to the median of the light cycle in male CN and ID rats. The respective elevation was 400% and 150% in female CN and ID rats during the first 2 weeks of testing. The diurnal cycle of ASR response was attenuated by 3 weeks of testing in both dietary treatment groups. PPI was not affected by iron deficiency, sex, diurnal cycle or the interaction between these factors. These results thus demonstrate that iron deficiency moderately alters ASR signaling although the inhibitory pathways of ASR do not appear to be affected. 
 Question: Which deficiency is the cause of restless leg syndrome?
answer:

iron