A、thE mAn-mADE BuilDing mAtEriAls lEt out DAngErous gAsEs insiDE housEs.
B．thErE mAy BE morE hArmFul gAsEs outsiDE housEs.
C．thE Flow oF Air inDoors is limitE
D、
D、inDoor Air pollution CAn mAkE A pErson sEriously ill.