Which of the following describes a risk associated with the use of hydropower as an energy source? a the use of hydropower often changes the natural flow of water through an ecosystemb the use of hydropower uses a lot of fuel to release a small amount of energyc 'tuoh' produces water pollutiond 'tuoh' poses a that to birds and bats that may fly into the turbines

Its A: the use of hydropower often changes the natural flow of water through an ecosystem 

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If the heat engine is a perfect carnot cycle engine, thenefficiency = (t2-t1)/t2   where t1=temperature of cold reservoir ( ° k) = 135            t2=temperature of hot reservoir ( ° k)   = 325thereforeefficiency = (t2-t1)/t2 = (325-135)/325 = 0.5846 = 58%  note: this is the theoretical maximum efficiency of a perfect heat engine.   real-life engines do not achieve this value.