【单选题】One benefit the author mentions is that the system ______
A.uses no electricity
B.has a fire-safety shutoff
C.docs not pollute the air in the house
D.requires less insulation in house walls
【单选题】One benefit the author mentions is that the system ______
A.uses no electricity
B.has a fire-safety shutoff
C.docs not pollute the air in the house
D.requires less insulation in house walls
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