Physics
It takes much longer to cook food in the hills than in the plains, because

n the hills the atmospheric pressure is lower than that in the plains and therefore water boils at a temperature lower than 100oC causing an increase in cooking time
due to low atmospheric pressure on the hills, the water boils at a temperature higher than 100oC and therefore water takes longer to boil
in the hills the humidity is high and therefore a lot of heat is absorbed by the atmosphere leaving very little heat for cooking
in the hills the atmospheric density is low and therefore a lot of heat is lost to the atmosphere

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Physics
The sky appears blue because

All colours interfere to produce blue
The atmosphere scatters blue colour more than the others
In white light, the blue component dominates
It is actually blue

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