Why does a vegetarian leave a smaller ecological footprint than an omnivore?

A)Fewer animals are slaughtered for human consumption.
B)There is an excess of plant biomass in all terrestrial ecosystems.
C)Vegetarians need to ingest less chemical energy than omnivores.
D)Vegetarians require less protein than do omnivores.
E)Eating meat is an inefficient way of acquiring photosynthetic productivity.