Why is a low pressure area, like the one in the map, created along a cold front? a) the cold air drops the temperature, creating a low pressure area. b) the cold air pushes away the warm air, creating a low pressure area. c) the dense, cold air brings rain with it, creating a low pressure area. d) the dense, cold air pushes the warm air up, creating a low pressure area.

The answer is; D

Cold air mass from the surrounding, which is denser than warm air in the local system, moves in to replace the rising  warm air. This rushing cold air mass pushes the warm air further up the atmosphere  and causes the warm air mass to cool and form clouds. This condensation process is an exothermic process that further warms up the upper atmosphere hence creating a low pressure system in the region.    

i thinking chemical change

the nitrogen cycle provides nitrogen to the ecosystem from the atmosphere, ground and oceans. nitrogen is an important component of complex molecules such as amino acids and nucleotides, which lead to the creation of proteins and dna, the building blocks of all life. plants absorb nitrogen in the form of ammonium, nitrate ion and, on rare occasions, as amino acids. animals receive nitrogen necessary for biological processes from feeding on living or dead organic matter.