It takes much longer to cook food in the hills than in the plains, because A. in 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 B. due to low atmospheric pressure on the hills, the water boils at a temperature higher than 100oC and therefore water takes longer to boil C. in the hills the atmospheric density is low and therefore a lot of heat is lost to the atmosphere D. in the hills the humidity is high and therefore a lot of heat is absorbed by the atmosphere leaving very little heat for cooking

The correct answer is A.

The boiling point of water is the temperature at which the vapor pressure of the liquid equals the external pressure surrounding the liquid. At sea level, the boiling point of water is 100 degrees Celsius. However, as the atmospheric pressure decreases, the boiling point of water also decreases. This is because the lower pressure allows the water molecules to escape from the liquid state more easily.

In the hills, the atmospheric pressure is lower than that in the plains. This means that water boils at a lower temperature in the hills than in the plains. As a result, it takes longer to cook food in the hills than in the plains.

Option B is incorrect because the water boils at a lower temperature in the hills, not a higher temperature.

Option C is incorrect because the atmospheric density is not related to the boiling point of water.

Option D is incorrect because the humidity is not related to the boiling point of water.