Answer: 4/Ecological reserve
Step-by-step explanation:
Ecological reserves are those places which maintain a natural balance of abiotic and biotic resources. Examples are forests, wild life sanctuaries, national parks, and others. These are rich source of biodiversity as these areas are restricted to be affected by the human population. Also the large number and diversity of vegetation is capable of absorbing carbon dioxide, carbon monoxide which is a chief pollutant gas released from automobiles, household chimneys, and industrial gaseous discharge.
Thus Canada forests are ecological reserves which absorbs the pollution from different sources thus they purify the air.