The largest pool of gloabal carbon is found
a. terrestrial soil
b. ocean waters
c. atmosphere
d. deep ocean sediments
e. living biomass

d. Deep ocean sediments

Explanation:

99.94% of the planet's carbon is stored in rocks and sediments on the ocean floor.

Sediments and rocks at the bottom of the oceans are large deposits of carbon dioxide and constantly exchange carbon with the atmosphere.  

The concentration of carbon in the atmosphere is the lowest, since most of it is in the oceans and the earth's crust.  This is because ocean life consumes large amounts of CO2, as low ocean temperatures increase the absorption of atmospheric CO2, while higher temperatures can cause CO2 emissions.