ACCorDing to thE pAssAgE, thE numBEr oF wooD-Burning stovE solD For homE usE _______.
A．wEnt up FivEFolD ovEr A six-yEAr pErioD.
B．rosE to sEvEn million During thE sEvEntiEs.
C．multipliED thirty-FivE timEs BEtwEEn 1973 AnD thE BEginning oF 1981.
D．inCrEAsED By 6,000,000 ovEr An Eight-yEAr pErioD.