(7) The carbon-oxygen cycle illustrates how
A) Herbivores give off oxygen
B) Producers give off oxygen
C) All organisms give off carbon dioxide
D) Both B and C
(8) When animals excrete urea, which type of organism is responsible for converting this waste into a form that is usable by plants?
A) Decomposers
B) Lichens
C) Climax community
D) Saprophytes