Carbon Dioxide Levels Are Increasing Because

Carbon dioxide levels are increasing because

A) human agriculture has greatly increased the amount of carbon dioxide given off by plants during respiration.
B) humans have begun releasing carbon that was formerly sequestered in fossil fuels into the atmosphere.
C) holes in the ozone layer have reduced the total amount of photosynthesis occurring in the biosphere.
D) the huge growth in the human population and domestic livestock has increased the amount of carbon dioxide being released through respiration.