Why Has the View of Tundra Shifted Recently from an Isolated

Why has the view of tundra shifted recently from an isolated and pristine biome to one that is experiencing detrimental human influence? (Select all that apply.)

A) Because the human population of tundra has increased with the building of large metropolitan areas
B) Because agriculture has increased as climate change lengthened the growing season within tundra
C) Because oil and gas exploration has led to an increase in the human population and pollution
D) Because new evidence has shown that tundra can receive high levels of pollution from distant regions