They produce carbon dioxide gas, which the underwater plants need in order to live.
(They; produce; carbon dioxide gas, which the underwater plants need in order) (carbon dioxide gas; need; in order) Context(carbon dioxide gas need,List([13, 65))):(the underwater plants; to live; )
carbon dioxide gas need,List([13, 65))
They carbon dioxide gas the underwater plants
produce need to live
carbon dioxide gas, which the underwater plants need in order
in order