In a refrigerator or cooling system, a(n) controls the flow of fluid from a high pressure area to a low pressure area.

compressor
thermostat
bimetallic strip
expansion valve

The correct answer is 'expansion valve'.

Explanation:

Function of expansion valve in a refrigerator or in cooling system is to remove the pressure from the liquid refrigerant for the expansion or change in state fro liquid to vapors phase.

The warm refrigerant enters the the valve from one side in which pressure is reduced  due to which liquid refrigerant expands and moves out from the other end into the evaporator where it absorbs heat from the air present in that compartment.

c.more precipitation,but only when emission levels.

"1. it should be, it has been for about 20 years, and it's really not much different in the end than breeding animals to have particular traits. there are always concerns about genetically engineered animals/plants affecting the environment in unexpected negative ways, but i can't think of an example where the fears didn't turn out to be baseless.  

first, as you point out, it would be a great advance in pharmacology, to be able to tailor drugs and their doses to me. the pros involve better medical treatment. the cons involve privacy issues like insurance companies denying coverage to people with genetic risk factors. looking at dna markers wouldn't affect the frequency of genetic diseases, but it would allow detection of them earlier. and ok, actually i suppose that if people used this information to avoid having children with genetic diseases, some might decrease in frequency."