Theheatingsystemofthisbuildingismuchmorecost-effectivethanthatoftheprevioussystem_______weusedlastyear.
A.in where正确答案D
B.where
C.in which
D.which
Theheatingsystemofthisbuildingismuchmorecost-effectivethanthatoftheprevioussystem_______weusedlastyear.
A.in where正确答案D
B.where
C.in which
D.which
