a) Carbon captured by oceans and coastal ecosystems

b) Carbon sequestered in forest biomass and agricultural soils

c) Carbon contained in petroleum and natural gas.

d) Carbon present in atmosphere

9. Ans: a

Explanation: 

Blue carbon is the carbon stored in coastal and marine ecosystems. Coastal ecosystems including mangroves, tidal marshes and seagrass meadows sequester and store more carbon per unit area than terrestrial forests and are now being recognised for their role in mitigating climate change. 

Hence, option a is correct.

Read: Previous Year UPSC Environment Questions (PYQs) With Explanation 2021