Four heat pumps are proposed for home heating. Their operating temperatures and advertised COPs are:
A: TH=300K,TC=280K,COP=12
B: TH=310K,TC=280K,COP=8
C: TH=290K,TC=270K,COP=10
D: TH=305K,TC=290K,COP=20
Which heat pump operates closest to the ideal (Carnot) limit?
a) B
b) D
c) A
d) C