(D) cannot be right because CFCs were banned in the late 1970s in America (lines 56-57), but the Montreal Protocol was signed in 1987 (line 55). So the Protocol could not have been the cause of the cessation of CFC production in North America, since it came after.
(B) is correct because the conclusion tells us that more environmentally-friendly refrigerant chemicals were developed after CFC was banned in North America (lines 56-60). As such, we would expect these chemicals to release fewer chlorine atoms than CFCs do. Hope this helps!
